Add links to filter documents by type

Currently, in the web UI, if the user wants to filter by document type (issues, other documents, etc.), they need to add terms such as type:issue or type:document to the search query. The casual user is not going to learn this search query syntax, and this is going to lead to a lot of confusion. It would be much better to add links to quickly filter by document type. These links will be graphical aids that any user can click with ease.

This is implemented now.

(made with skribilo)