e-util: Port to thread-safe ECategories API

This ports the following two function calls throughout Evolution:
 • e_categories_get_list() to e_categories_dup_list()
 • e_categories_get_icon_file_for() to e_categories_dup_icon_file_for()

It necessarily changes some internal e-util API:
 • e_util_get_searchable_categories() to
   e_util_dup_searchable_categories()

This bumps the EDS requirement to 3.13.1.

https://bugzilla.gnome.org/show_bug.cgi?id=727221