The JS for the group share page failed to load
because of an incorrect comparison of the result
of String.match() against a number and also
because of an attempt to load Bootstrap
unnecessarily on this pages.

This commit fixes the issue and prepares us for
adding new pages in future by:

 * Adding a client-side micro-router to simplify running
   page-specific JS

 * Only loading the Bootstrap components on pages that
   actually need it.

Fixes #2867