* Add API support for labels.

* Error handling for adding/replacing multiple issue labels

* Revisions to function names and error handling. Use issue.ClearLabels in replace/clear functions

* Additional code cleanup

* Lighter icon colors for repo files

* also color submodule icon

Enable/disable input based on user chosen options for wiki and issue tracker.

* Add support for .diff and .patch

Add the ability to get text-diff and format-patch by adding .diff or
.patch in the end of a commit url. Issue #2641

* models: git_diff: various fixes

* Renames commitId to commitID.
* Writes stderr to a bytes.Buffer and displays proper error message on
command failure.
* Various style changes.

Signed-off-by: Dennis Chen <barracks510@gmail.com>

If anonymous (not signed in user) requests page
"/:owner/:repo/pulls" he gets an error:

  template: repo/issue/list:11:105: executing "repo/issue/list" at <.PullRequestCtx.Base...>: nil pointer evaluating *models.Repository.Link

This commit fixes that.

Signed-off-by: Dmitry Yu Okunev <dyokunev@ut.mephi.ru>

Since the release struct is initialized with the current `HEAD` of the
current `release.Target` the commit id has to be updated if the tag
commit already exists. Otherwise the linked commit on the release page
will target the current `HEAD` at release time.

When calculating the current behind commit count the calculation should
use the current release target to get the total commit count. Should the
release target not exist anymore the calculation will return zero for
the newest release on that target. Older releases on that target will then
use that calculated commit count as reference.

The only use case that is now somehow invalid is when the release target
was merged / deleted after a tag on that release target:

    master 1 - - - - - - - 6
            \             /
    branch   2 - 3 - 4 - 5

When `4` is the last tag on branch `branch` and the branch `branch` is not
yet deleted the calculated numbers would be:

    1 commits to branch since this release

Now if the branch `branch` gets deleted the calculation function will not
find the branch and use the commit count of the newest release (`4`) as
reference resulting in:

    0 commit to branch since this release

This fixes #3326

Unix() already uses UTC as timezone

Add sign in check before check user account level

os.Rename does not create parent directory automatically when not exist

* Added coding style modes to SimpleMDE

* Moved the CodeMirror addon from simplemd to codemirror directory