Combine Snippets and Attachments

Created by: riyad

Combine the "Attachments" and "Snippets" tabs for projects and turn it into something more general. A user could choose to either add a code snippet (text files) or upload a file (anything else). It could later be referenced/used it in other places in GitLab (e.g. Comments, Wiki).

The "attachments" are problematic at the moment, because you can't really add anything. It's just a collection of what people have attached to notes.

• The Ace editor could be used for highlighting, when editing text files. (see #2156 (closed))
• Those Snippets/Attachments should be offered for download.