Move most of the EE-specific LDAP code to EE-specific classes/modules

This will prevent or reduce merge errors. This doesn't include *all* of the EE-specific LDAP code, but it's the low-hanging fruit. I will get the less-straightforward stuff in a subsequent merge request to avoid making this one unbearably large. 

## Why is this necessary?

I'm starting work on some of the priority LDAP features/fixes. I was about to start stuffing additional EE-specific methods into `Gitlab::LDAP::Adapter` and it felt like this could be a CE-EE merge danger zone. This seemed like a potentially quick fix to that worry so I thought I'd take a moment to see if it was sane. 

@DouweM and I talked briefly about this. It seems to be the way we want to go in the future anyway so this gets the ball rolling. 

If this goes through and everyone is happy, I'll also create a subsequent merge request to add some development docs about organizing EE code. 

FYI @vsizov @jacobvosmaer-gitlab 

See merge request !511

Add license breakdown to admin pages

Screenshots:

At the top of the overview page:

![image](/uploads/48d489f905b9eee09a3bf038bcf33244/image.png)

At the bottom of the license page:

![image](/uploads/969caa48e98af4d9afb400b9e5b1b5fd/image.png)

Closes #653

See merge request !516

Remove unused JiraIssue class and replace references with ExternalIssue

Fixes https://gitlab.com/gitlab-org/gitlab-ee/issues/739

This MR can be considered as a fix of wrong CE->EE merge (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4659)

See merge request !545

Closes #653

Add example of MR error msg due to file locking

[ci skip]

See merge request !544

Fix typo and change URL of custom hooks doc in main README

Partially includes https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5169

See merge request !542

[ci skip]

CE upstream



See merge request !543

Refactor file lock documentation

- Add permissions section
- Add example pre-receive hook message
- Replace outdated images

See merge request !541

- Add permissions section
- Add example pre-receive hook message
- Replace outdated images

[ci skip]

Make subnavigation a bit darker color



See merge request !5166

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Update ui_guide.md with button capitalize rule

cc @jschatz1 @hazelyang @skyruler 

See merge request !5161

Update New Snippet buttons.

## What does this MR do?

No longer shows New Snippet button to users who aren't able to create a new snippet in the given context.

Also removes the plus icon from the New Snippet buttons, as they're no longer used in other creation buttons.

## Are there points in the code the reviewer needs to double check?

Make sure the snippets pages don't break or show the buttons to users who shouldn't have access to them.

## Why was this MR needed?

Users that weren't logged in would click the New Snippet button and get a 404 error. You would also get 404 errors from the New Snippet button on project snippets for projects you weren't able to create snippets for.

## What are the relevant issue numbers?

Fixes #14595.

## Screenshots (if relevant)

Before:

![before1](/uploads/2c222cd981332d30772054cefadafa28/before1.png)

![before2](/uploads/2734f8a84ae293b08dd982f2ed7da028/before2.png)

After:

![after1](/uploads/c84aa9aec17056095271b0f24c6e9b5b/after1.png)

![after2](/uploads/70fe37ad7be5054bf20439ca0a1f5ccc/after2.png)

![after3](/uploads/afcd435c211482e9df25cb8971f1e65e/after3.png)

![after4](/uploads/9eab87440aae4991b508373ff36e3c7a/after4.png)

![after5](/uploads/f5ec167cb3e1115d3b3a43bd5231bc60/after5.png)

![after6](/uploads/c774cbb1f9babe3382ff69af7060b9c5/after6.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4998

No longer shows New Snippet button to users who aren't able to create a new snippet in the given context.

Also removes the plus icon from the New Snippet buttons, as they're no longer used in other creation buttons.

Fixes #14595.

Split Cropper.js from the main JavaScript manifest.

## What does this MR do?

Splits Cropper.js from the main JavaScript file.

## Are there points in the code the reviewer needs to double check?

That the avatar uploader works. (It did in my testing)

## Why was this MR needed?

Smaller JS payload.

## What are the relevant issue numbers?

#14372 

## Does this MR meet the acceptance criteria?

- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !4978

Add min attribute to projects_limit field on user's form

This PR adds `min=0` attribute to `:projects_limit` field on user's form in the admin panel. It improves UX disallowing user to enter negative values in this field.

![](http://take.ms/70V8W)

See merge request !3622

Prevent stale data in LDAP group sync last owner check

Representing https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/529

Fixes gitlab-org/gitlab-ce#17764

Turns out that switching to an AR association has resolved the issue. However, a merge problem from CE to EE caused the owners method to not be removed so it took precedence over the association. This removes that method and adds a test to ensure we don't have stale owner data in the future. 

See merge request !531

Fix gemfile

1. replace `"` to `'` in Gemfile.

2. change `require: nil` to `require: false`.
`require: nil` and `require: false` get same result, but i think we shouldn't write it differently in other places.

3. set version for gems.
better gem's version control for prevent dependency errors.

See merge request !5078