* Update Financial Assistance logic

Use the zendesk proxy app instead of the unsupported zendesk library.

* Move to pre-fetching the group IDs.

Rather than making extra requests to zendesk to list all groups and find
a specific group ID. Just make a pre-filled list of group IDs for the
groups we care about.  When a group name is passed in, it is checked
against this list and the ticket is created in the correct group so the
right people can respond to it.