* Use commit objects instead of IDs when generating diffs
* Use proper references when generating MR's source and target
* Update broken specs

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

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

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

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

Since GitHub doesn’t apply these constraints to theirs wiki slug
allowing characters like `,`, `:`, `*`, etc, we need to relax our
constraints or some wiki pages will not be available after they were
imported.

For an example the Devise project have a wiki page with the following
slug: “How To: Add sign_in, sign_out, and sign_up links to your layout
template”

Added also a `Gitlab::Ci::Build::Artifacts::Metadata::ParserError`
exception class.

This changes the format of metadata to handle paths, that may contain
whitespace characters, new line characters and non-UTF-8 characters.

Now those paths along with metadata in JSON format are stored as
length-prefixed strings (uint32 prefix).

Metadata file has a custom format:

1.   First string field is metadata version field (string)
2.   Second string field is metadata errors field (JSON strong)
3.   All subsequent fields is pair of path (string) and path metadata
     in JSON format.

Path's metadata contains all fields that where possible to extract from
ZIP archive like date of modification, CRC, compressed size,
uncompressed size and comment.

This is needed because of backward compatibility. Previously artifacts
archive had `.tar.gz` format, but artifacts browser requires ZIP format
now.

`artifacts?` method checks if artifacts archive is available.

This support is not completed though, as parent directory that is first
in collection returned by `directories!` is not iterable yet.

This implementation makes it possible to browse artifacts, it
depends on artifacts metadata.

This reverts nesting artifacts controller in builds module.

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

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

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

Improve the consistency of commit titles, branch names, tag names, issue/MR titles, on their respective project pages

See https://gitlab.com/gitlab-org/gitlab-ce/issues/4183

Closes #3046