Show a random Markdown tip in the textarea placeholder

cc @darby

See merge request !879

Removed the icons from the New Issue and New Project buttons

Fixes #1869

No more icons!

See merge request !885

Change the default admin password

Closes internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2422

See merge request !865

Performance improvements

* store @participants in variable
* store result of subscribed? call into variable

In total it reduce amount of SQL queries for issue or merge_request with 10 comments/participants almost twice.

See merge request !883

Add 2FA status to user admin API

This MR adds the `two_factor_enabled` field to the admin's API to indicate whether a given user has enabled 2FA.

See merge request !881

Updated merge request merged web hook to correctly fire action=merged.

I believe this merge request will fix both issues #879 and #498.

If a merge request was merged via the command line, the correct web hook was fired with the field `object_attributes.action = "merge"`. However, if the merge request was merged via the web UI, the webhook would be fired with `object_attributes.action = "open"`.

See merge request !780

Fixes #879
Fixes #498

Explicit error when commit not found in the GitLab CI

!!! SHOULD BE MERGED WITH https://gitlab.com/gitlab-org/gitlab-ci/merge_requests/159

https://dev.gitlab.org/gitlab/gitlab-ci/issues/280

See merge request !871

stop jumping all content on collapsing and expanding the sidebar

When you collapse or expand the sidebar, all content shifts with 5px.

This merge request solves that.

cc @darby

See merge request !1877

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

* store @participants in variable
* store result of subscribed? call into variable

In total it reduce amount of SQL queries for merge_request with 10
comments/participants twice.
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

* store @participants in variable
* store result of subscribed? call into variable

In total it reduce amount of SQL queries for issue with 10 comments/participants twice.
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

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

Only look up Commit authors/committers by email

- Removes looking up authors/committers by name
- Renames `User.find_for_commit` to `User.find_by_any_email`

Closes #1850

See merge request !878

Updated the categories of Application Settings Form

Changed the categories and order of the application settings accessible by admin/application_settings

Link to issue: https://dev.gitlab.org/gitlab/gitlabhq/issues/2412
Issue will be closed upon approval of this merge request.

Fixes #2412

See merge request !877

Allow user to remove public email address

Closes internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2419

See merge request !880

Closes https://github.com/gitlabhq/gitlabhq/issues/9391

- Removes looking up authors/committers by name
- Renames `User.find_for_commit` to `User.find_by_any_email`

Create SSH keys document

@job I created the next document for your review, which is "Creating your SSH Keys"

Thanks!

See merge request !1875

added link to GitLab Basics

Added link to GitLab Basics

See merge request !1876

Revert README avatar to original version

In my attempt to rid the world of `gitlab_logo.png`, I didn't realize that http://about.gitlab.com was hosted somewhere else and hence the original link worked fine.

See merge request !876