browse: Improve origin-dependent browsing and add release view

This commit improves origin-dependent browsing of the SWH
archive by updating the design but also providing quick links
to the following objects in origin-dependent views: root
directory of the default branch, list of branches and list of
releases. These links depend on the SWH visit date selected
by the user.

A dedicated view for displaying the metadata of a SWH
release has also been introduced.

Some code refactoring has also been performed in order
to factorize some common processing in origin-dependent
browsing and thus remove code duplication.

Closes T931
Closes T932