Added a configurator for Glacier repositories to the webapp. That was the last
cloud repository configurator that was listed in the webapp and wasn't
done. Indeed, just two more repository configurators remain to be filled in:
phone and NAS.

By default, Glacier repositories are put in a new "small archive" group.
This makes only files placed in "archive" directories be sent to Glacier
(as well as being dropped from clients), unlike the full archive group
which archives all files. Of course you can change this setting, but
avoiding syncing all data to Glacier seemed like a good default, especially
since some are still worried about Glacier's pricing model.

Fixed several bugs in the handling of archive directories, and 
the webapp makes a toplevel archive directory when an archive remote is
created, so the user can get on with using it.

Made the assistant able to drop local files immediately after transferring
them to glacier, despite not being able to trust glacier's inventory.
This was accomplished by making the transferrer, after a successful upload,
indicate that it trusts the remote it just uploaded to has the file,
when it checks if the file should be dropped.

Only thing left to do for glacier is to make the assistant retry failed
downloads from it after 4 hours, or better, as soon as they become
available.