Separated the directives into two separate modules

This was necessary because some of them must be made available
for the displayer page, and possibly other pages, too,
but some other directives depend on annotator, which is only present
in the main app.

Therefore, no we have
 - the h.directives angular module for the small, independent directives, and
 - the h.app_directives angular module, which currently only holds the
   annotation directive.