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

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