* 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

* 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>

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.

Unix() already uses UTC as timezone

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

Sets all avatars to use PNG image format.
Keeps avatars consistent at 290x290px resolution.

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

Fixes relative urls coming from api/v1

See https://github.com/drone/drone/issues/1701

RepoLink -> Link, RepoRelLink -> RelLink, FullRepoLink -> FullLink

Executed go fmt

getEngine() not handles DB parameters (#2972) (#2974)

Uses .AllCols() for Update in updateMirror()

Spanish traslation removed

Fixed a wrong way to ommit the --prune option in process.ExecDir() for MirrorUpdate function

Re: issues gogits/gogs#2863 and gogits/gogs#3231

As a result of modifications to the contents of the conf folder, `make bindata`
was run, causing an update to bindata.go.

Meta
-----
This commit will be rebased onto the 'develop' branch.

This prevents user retrieve arbitrary webhook by changing URL to
access webhook from other unauthorized repositories.

Since . and .. has browser automatical behaviors, we need to disallow those names.

Initially proposed by #2376 and fixes #3068 as well.

- Arbitrary file creation leading to command execution
- .md file creation/deletion

Reported by Gabriel Campana.

Closes #2764

Also changes the avatar from a jpeg to a png, to allow for
transparent background. The indexed png is also smaller in size.

Note that at the moment the default avatar is only used when
the user requested a custom avatar and the custom avatar file
is not found (should never happen).

In the future the default avatar could be used as a default
return when by-mail avatar lookups fail too (both gravatar
and libravatar support passing a default)

use 'official' repo.Name instead of incoming repoName; to enforce
correct capitalisation

Add start count corrector for Repository.NumClosedIssues