Handle nil restricted visibility settings

Return `true` from `non_restricted_level?` when the `restricted_visibility_levels` setting is nil.  This addresses #2154.

cc @sytse

See merge request !1724

Return `true` from `non_restricted_level?` when the
`restricted_visibility_levels` setting is nil.

This reverts commit 7602cef5.

Fix condensed range in MR push comment.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/1246

In https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/326#note_984907, you see that the compare page doesn't actually have 39 commits because we're using `first_new_commit^`, which is not always the same as `oldrev`. With this MR, we use `oldrev` instead, which will always work.

See merge request !1721

Api: sort merge_request comments

Add default_scope { order(created_at: :asc, id: :asc) } in Note so comments are sorted when fetched through api.

See merge request !256

Add changelog, license and contribution guide links to project sidebar.

If the version is known, the "Version: 7.9.0pre" button links to the changelog, otherwise a "View changelog" button is shown.

![Screen_Shot_2015-03-18_at_14.22.29](https://dev.gitlab.org/gitlab/gitlabhq/uploads/747acc018ec9a188098e0f0bc4e91cc3/Screen_Shot_2015-03-18_at_14.22.29.png)

See merge request !1708

Bump gitlab_git to 7.1.2

For https://dev.gitlab.org/gitlab/gitlabhq/issues/2151

See merge request !1722

List new commits for newly pushed branch in activity view.

When someone pushes commits, I want to see them, regardless if it's a new or existing branch. If it's a new branch, we compare with the default branch (usually master).

![Screen_Shot_2015-03-17_at_15.49.13](https://dev.gitlab.org/gitlab/gitlabhq/uploads/4cb7e0d833bc83a30197db81d4b273bc/Screen_Shot_2015-03-17_at_15.49.13.png)

See merge request !1711

Fix the order of signin and signup on features page.

See merge request !1720

Extend commit calendar to actually show what commits were made on a date

## What does this MR do?
This MR extends the commit calendar so it acutally shows what commits were made on a date and in which project.
It is based on the optimizations @dzaporozhets made for the calendar.

## Are there points in the code the reviewer needs to double check?
The UI and how the links are generated i guess. That feels hacky at the moment :/

## Screenshot:
![commit_calendar_extend_display](https://gitlab.com/uploads/gitlab-org/gitlab-ce/5bf1631660/commit_calendar_extend_display.png)

I assume that i have to refactor this a bit more to make it a cleaner implementation, so please give me feedback on what needs to be changed :)

See merge request !326

Enable line wrapping per default.

This MR enables line wrapping by default and removes the checkbox to toggle it.

Let's be honest, noone likes horizontal scrollbars.

/cc @dzaporozhets @DouweM As discussed yesterday. Please take a look. Did I miss something?
The change feels to easy 😄

See merge request !396

Fix public issue

See merge request !1717

Add support for external wikis

## What does this MR do?
This MR adds the possibility to replace the link to the internal wiki of gitlab with a custom link.
Currently this is realised as a service.

## What Use Case does this MR solve?
In my Company we already have a wiki System (Confluence).
We have a policy to use the existing wiki, so we can't switch to the internal wiki Gitlab provides.
This currently only leaves us two choices:
1. Disable the gitlab wiki. That means we completly loose the connection between wiki and code from the gitlab ui.
2. Create a simple wiki page with a link to our external wiki and hope that no one uses the internal one.

Both solutions are not really good.
So what can be done to improve the situation while making it as easy as possible for new developers to access both, wiki and gitlab?
Replacing the wiki link kinda like the JIRA integration replaces the issues link looks like a good first step to me. :)
This can probably be extended later to completly prevent access to the internal wiki (currently that's still possible if you know the link) or maybe to check if the link really points to a wiki.

## Screenshot:
![external_wiki_service](https://gitlab.com/uploads/gitlab-org/gitlab-ce/89b27cf068/external_wiki_service.png)

See merge request !291

More actively use css variabled to prevent colors duplication

See merge request !1715