* FIX: allow editing in composer before a category is selected
If the site setting `allow_uncategorized_topics` is disabled, but no site categories have a topic template, the textarea of the composer should be enabled. This allows for a post body to be entered, however the post/topic should not be successfully created until a category is selected.
If `allow_uncategorized_topics` is disabled *and* one or more categories have a topic template, the textarea of the composer should remain disabled until a category is chosen (so that the body of their post isn’t overwritten by the template).
* Avoid recalculating hasTopicTemplates repeatedly
Admins can currently add the bookmarks discovery route link
to the homepage interface, but users can't presently select
that as their default home view. This change facilitates that,
adding the option to the existing Default Home Page dropdown on
the User Preferences Interface page.
