Adds a loading state to prevent multiple requests when clicking the
drafts menu button.
We are also making a very slight adjustment to button spacing (needed
for both desktop and mobile).
This change adds a new dropdown trigger next to the "New Topic" button.
When clicked a menu will display a list of topic/post drafts that can be
clicked to resume the draft within the composer.
The "New Topic" button will no longer change text to show "Open Draft"
when a draft topic exists, it will still attempt to load the existing
draft if one exists (this will change later when we support multiple
drafts in a separate PR).
The "My Posts" link in desktop sidebar will now be "My Drafts" and only
appear when the current user has existing drafts.
