Handle question posts from comments service
Clean up dead forums front-end code
Unify forum thread views (and templates)
Distinguish forum thread types in rendering

Each thread's type is now included in its post details, and question
threads have marked answers shown immediately below the body of the
initial post.
Add endorsement info to marked answers in forum
Change endorsement UI for forum question threads

Responses to question threads can be "marked as answer" instead of
"endorsed".
Re-render forum responses when marked as answer
Add post type indicators to forum sidebar nav

The previously existing checkmark for threads with endorsed responses is
removed, as it is mostly redundant.
Add post type control to forum new post form

Also change server to pass post type through to the comments service.
Refactor a small amount of forum permission code
Allow authors of forum questions to mark answers
Hide comments in marked answers in forum questions

A link to show the comments appears in their place.
Merge pull request #4506 from edx/gprice/forum-question-type

Add initial front end handling of question threads