Consolidate functions dealing with Google Accounts and look-up of User entities
into a single site-wide controller module. Tests will be added in a subsequent
commit as soon as Google App Engine tests using mocker are figured out.
Patch by: Todd Larsen
Review by: to-be-reviewed
Exception classes used by controller logic to request an "out-of-band" response
be displayed by the view instead of what the view would normally display.
Patch by: Todd Larsen
Review by: to-be-reviewed