spinner.gif and spinner-on-grey.gif are the same file.
Explicitly give the LMS a spinner.gif file.

OPEN-328

The actions are now consolidated in one location for each piece of
content. Primary actions (vote, follow, endorse, mark as answer) are
buttons, and secondary actions (pin, edit, delete, report, close) are in
a menu. This also includes improved front-end error handling for the
actions and significant test cleanup.

Co-authored-by: jsa <jsa@edx.org>
Co-authored-by: marco <marcotuts@gmail.com>
Co-authored-by: Frances Botsford <frances@edx.org>
Co-authored-by: Brian Talbot <btalbot@edx.org>

The menu allows filtering to unread, unanswered, or flagged threads.
This includes passing through the appropriate query parameters to the
comments service.

A link to show the comments appears in their place.

Co-authored-by: jsa <jsa@edx.org>

Also change server to pass post type through to the comments service.

The previously existing checkmark for threads with endorsed responses is
removed, as it is mostly redundant.

Responses to question threads can be "marked as answer" instead of
"endorsed".

Co-authored-by: jsa <jsa@edx.org>

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 help text to several fields, update visual styling, and make it
appear in the right-hand pane of the discussion tab instead of sliding
down from the top.

Co-authored-by: jsa <jsa@edx.org>
Co-authored-by: marco <marcotuts@gmail.com>

Now that the sidebar class is no longer used, many rules no longer need
!important and can move out of _shame.scss.

This will enable much cleanup of the relevant SASS rules.

The filter box will now remain fixed while the rest of the menu scrolls.
This also fixes a minor cosmetic bug in which the thread list would
overflow its container if the user opened the browse menu, scrolled the
page, and then closed the browse menu.

The home button is removed, the search box is always displayed, and many
visual adjustments are made, along with a large amount of refactoring.

Originally reviewed in #4211

Thread entries now show an activity count that includes the original
post, and only one of the vote count and activity count is displayed
based on the user's selected sort. The sorting and filtering options now
both use a select and are somewhat more verbose, and the visual styling
of the sort/filter bar is updated.

Originally reviewed in #4165 with a bugfix in #4211

A thread will be labeled if it is pinned, if the user is following it,
or if it was authored by a staff member or community TA. This also
slightly changes the color used for community TA labels.

Originally reviewed in #4072

Use larger and lighter title font, decrease padding, and use lighter
solid backgrounds instead of gradients. Also, refactor SASS code to
conform better to our new style, including using more specific class
names.

Originally reviewed in #4072

JIRA: FOR-627

Co-authored-by: Brian Talbot <btalbot@edx.org>

JIRA: FOR-591