Tweak forum topic browse menu

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.
Increase the test SQLite DB timeout. TE-397
Remove sidebar class from forum nav

This will enable much cleanup of the relevant SASS rules.
Clean up forum nav Sass

Now that the sidebar class is no longer used, many rules no longer need
!important and can move out of _shame.scss.
Add myself to AUTHORS.
Asset support in split
LMS-2876
Allow to_deprecated_string to do its magic
removing unused import
Make pictures smaller
Merge pull request #4324 from edx/dan-f/add-to-authors

Add myself to AUTHORS.
Merge pull request #4318 from edx/gprice/forum-sidebar-debt

Reduce tech debt in forum sidebar
Add revert_to_published method.

STUD-1860
Merge pull request #4343 from edx/mvo/removing_unused_action_chains

Removing unused import
Merge pull request #4294 from edx/split_mongo_assets_cherry

Split mongo assets cherry
Merge pull request #4317 from edx/zoldak/increase-sqlite-timeout

Increase the test SQLite DB timeout. TE-397
Move context_managers to base class, overridden by mixed.
Merge pull request #4344 from edx/christina/revert_to_published

Add revert_to_published method.
This emits enrollment mode changes events
Merge pull request #4309 from edx/nimisha/refactor_mixed_context_managers

Nimisha/refactor mixed context managers
Enables LMS to handle deprecated URLs

LMS-2651