Also fix a few places where page_404 should be render_404.

In this version we will support only relative paths in artifacts
metadata. Support for absolute paths will be introduced later.

Artifacts metadata field will be used to store a filename of gzipped
file containing metadata definition for given artifacts archive.

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

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>

Using the fuzzy filter, develop "file finder" feature.
- feedback(http://feedback.gitlab.com/forums/176466-general/suggestions/4987909-add-file-finder-fuzzy-input-in-files-tab-to-ju )
- fuzzy filter(https://github.com/jeancroy/fuzzaldrin-plus)
- shortcuts(when "t" was hitted at tree view, go to 'file find' page and 'esc' is to go back)
- depends on gitlab_git 7.2.22

Get "Merge when build succeeds" to work when commits were pushed to MR target branch while builds were running

Closes #4032

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