Better docstrings for FolderItem/ImapUid
Remove duplicate lower() call.

We already make sure all members of existing_labels and new_labels are
lowercase.
[SCHEMA] add inbox folder name cols to imapaccount
Add a backref to message to access associated imapuid
cleanups
pool_size arg went missing somewhere
MSGDIR changed names while I wasn't looking
IMAP sync backends now save folder names when sync starts.
Canonicalize All Mail to be 'archive' in our datastore
Canonicalize folder_names keys as lowercase

As a part of this, I'm also simplifying the logic in Gmail's
folder_names() detection to get rid of the janky usage of
boolean flags.
mg removed the add command
remove unused imports in inbox script
Update test dump for new ImapAccount columns
Make a note about ImapUid test entries