This commit adds a tracking dropdown to each individual thread, similar to topics,
that allows the user to change the notification level for a thread manually. Previously
the user had to reply to a thread to track it and see unread indicators.
Since the user can now manually track threads, the thread index has also been changed
to only show threads that the user is a member of, rather than threads that they had sent
messages in.
Unread indicators also respect the notification level -- Normal level thread tracking
will not show unread indicators in the UI when new messages are sent in the thread.
Major changes included:
- better support for screen readers
- trapping focus in modals
- better tabbing order in composer
- alerts on no content found/number of items found
- better autofocus in modals
- mini-tag-chooser is now a multi-select component
- each multi-select-component will now display selection on one row
This reverts commit 20780a1eee.
* SECURITY: re-adds accidentally reverted commit:
03d26cd6: ensure embed_url contains valid http(s) uri
* when the merge commit e62a85cf was reverted, git chose the 2660c2e2 parent to land on
instead of the 03d26cd6 parent (which contains security fixes)
