Notes:
* Don't store the g2->g3 map in the task; it gets too large and
overflows the context column.
* Import album sort orders
* Try to treat duplication in the summary and description fields
sensibly.
* Move the g2 import config page under the Settings menu
* Clean up the settings page slightly and send users to the
maintenance page to do the actual import (not an optimal UI, but it
works).