Imported some of the GPLv3'd changes from RhodeCode v2.2.5.

This imports changes between changesets 21af6c4eab3d and 6177597791c2 in
RhodeCode's original repository, including only changes to Python files and HTML.

RhodeCode clearly licensed its changes to these files under GPLv3
in their /LICENSE file, which states the following:
The Python code and integrated HTML are licensed under the GPLv3 license.

(See:
https://code.rhodecode.com/rhodecode/files/v2.2.5/LICENSE
or
http://web.archive.org/web/20140512193334/https://code.rhodecode.com/rhodecode/files/f3b123159901f15426d18e3dc395e8369f70ebe0/LICENSE
for an online copy of that LICENSE file)

Conservancy reviewed these changes and confirmed that they can be licensed as
a whole to the Kallithea project under GPLv3-only.

While some of the contents committed herein are clearly licensed
GPLv3-or-later, on the whole we must assume the are GPLv3-only, since the
statement above from RhodeCode indicates that they intend GPLv3-only as their
license, per GPLv3§14 and other relevant sections of GPLv3.

branch selectors: show closed branches too

It would be even better if they were fetched dynamically somehow and perhaps
placed in a sub sub menu ... but showing them in the list is often better than
not showing them at all.

added same switch to logic for tags and bookmarks containing /.
added "at" GET params to visualize switching for revisions with /

switch to branch: handle slashes in branch names

In git, having slashes in branch names are not uncommon.

We cannot use a branch name with slashes in the url, so in that case, we
use the changeset id instead like we already do for tags and bookmarks.

Fixes #654

Implements #304
hashes in relevant places are displayed using monospaced font.

lazy load of branches and tags menu
- to reduce load on repositories with large amount of branches and tags.
- reduce load times of pages significantly on large repos