Add topic selection to inline thread editing, fixing errors

this change puts the topic selection dropdown into the inline view for a thread when editing.  prior to this, the selector would be missing and any attempts to submit the form would fail.

this also solves a related issue where a javascript error prevented the rich text editor for the thread body from being properly rendered in the form.

@polesye @andy-armstrong please review
@jmclaus FYI

TNL-549


@jimabramson, I'd prefer that we don't adjust the styling in ``_create-edit-post.scss`` as its scope well defined as is in general. What we have been doing to compensate for poor LMS CSS architecture is updating the ``_shame.scss`` file with any overrides that are needed but shouldn't exist or be needed in a well defined CSS architecture.

I understand its additional rules in the rendered CSS, but I think calling out specific properties in this separate file has the following benefits:

1. It provides a central place we can look to when adding band-aids, less than ideal code, and temporary overrides
2. it provides a central place to look when its time to address FED debt, CSS re-architecture, and general cleanup
3. it doesn't muddy or conflate well-formed CSS architecture (such as the forums discussion styling you pointed to in this case).

If you feel strongly about not introducing this into the code, we can chat more about details and alternative solutions.