Increase images expiration time on Apache conf

10 years sounds OK, and definitely better than just 2 hours. If images
are regenerated then its filename will change, as it does for CSS or JS.
Docs: Move up the gzip compression in Apache conf sample

To align with Fabric Apache configuration sample.
Docs: Change comment for compression on Apache conf

Provide a better description since good docs will avoid us questions.
docs: use literalincludes for whole text files

.. literalinclude
http://sphinx-doc.org/markup/code.html#directive-literalinclude is a
much richer way of showing external files.
langpicker: Various UI fixes

See bug #3181
js: Update select2 to 3.4.5

One of the things we need most of all is diacritics support, for the
language picker.

See: https://github.com/ivaynberg/select2/issues/1472
breadcrumbs: Remove the style="visibility: hidden" from select2 menus

The select2 update takes care of doing this for us; if we leave it in
the initial style the select2 menu will copy it and the menu disappears.