Snippets: Revisions (commit history) accessible from the UI ("History" button)

Description

Currently, when you view a snippet there is no way on the user interface to see the history of changes.

Proposal

Snippets should have a "History" button that allows users to view the changes made to the snippet (or files therein).

This should ideally be aligned with the same feature in GitLab Wikis.

Side Note: Maybe worth pointing out, the Wiki currently provides a "History" button, but is still missing the "Compare" feature between history entries.

Similar or Related Issues

• https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5002 (Cannot diff changes in wiki history)
• https://gitlab.com/gitlab-org/gitlab-ce/issues/13426 (Version control for snippets)