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 allow post type to be passed through to the
comments service.