WebAPIToken.objects.get_or_create_client_token() can now be given a

Local Site for filtering or creating tokens, as well as a default

extra_data and a default token policy for new tokens. This gives

callers more control over the resulting token.
It also now takes a min_validity_secs, which specifies the minimum

time an existing token must be valid in order to be considered. This

defaults to 5 minutes, which should be a good minimum default for

anything that may need to perform an immediate operation. Callers can

pass in a longer validity window.

Unit tests pass.