Show tags in commit view

### What does this MR do?
With this MR you can see the assigned tags for a commit in the commit view.
### Are there points in the code the reviewer needs to double check?
I don't think so. But it would be awesome if the reviewer can tell me how to add a tag to the sample_commit in spec/support/repo_helpers.rb.
Then I can add a test for the new tag_names_contains method as soon as possible :)

### Why was this MR needed?
At the moment if one click on a commit will see details such as: parent commit, amount of additions, deletions, but will not see if this commit has Tag linked to it.
Showing branch, tag details will give better overview about the commit

### What are the relevant issue numbers / Feature requests?
Feature request: http://feedback.gitlab.com/forums/176466-general/suggestions/3962044-show-tags-in-commit-view
### Screenshots
![gitlab_feature_show_tags](https://gitlab.com/uploads/haynes/gitlab-ce/771c1a36bb/gitlab_feature_show_tags.png)

@dblessing Can you take a look at this MR as well please?

See merge request !297