Support for dynamic fields in REST serializer
bugfix - couldn't delete records using /action

General GET must be after checks for /delete, /update. GET modifying the
data is not pretty, but it's a great helper during development, since we
need to just type the URL in the browser
Don't save after task.pop().

If the task fails, it shouldn't be removed from the queue, instead
it should be rescheduled.
More useful exception message