Shift special folder priorities when synchronizing account

This patch solves two issues: (a) sometimes messages stick around in
conversations too long because Geary hasn't synchronized with Trash
(therefore realizing they should be blacklisted), and (b) All Mail can
take a long time to synchronize because of its bulk size.

This patch moves Trash (and Sent Mail) higher up in priority and moves
All Mail and Archive down to reflect these issues.