Add new AuthVector classes
Don't update the cache for an AKA vector
Call put_av from on_digest_change
Make the cache layer use a DigestAuthVector
Add AuthVectorHandler
Plumb authtype and autn through the code
Add missing file
Merge branch 'master' of github.com:Metaswitch/crest into aka_hss

Conflicts:
	src/metaswitch/crest/test/api/homestead/backends/hss/gateway.py
HSS updates for AKA
live test fixes
Various improvements to AKA support:

* Allow interop with an OpenHSS (which requires an authentication scheme of "unknown" not "Unknown")
* Cache the realm and QoP values returned from the HSS
* Record whether SIP-Digest is known to be the preferred authentication scheme configured in the HSS, and don't use the cached digest if not
Update DB schema
Indicate authentication type consistently
Merge branch 'dev' into aka_hss

Conflicts:
	src/metaswitch/crest/api/homestead/backends/hss/backend.py
	src/metaswitch/crest/api/homestead/backends/hss/gateway.py
Various minor fixes
Code review markups
Make tests pass again
Further code review markups
Don't put False in quotes
Merge remote-tracking branch 'origin/dev' into aka_hss

Conflicts:
	src/metaswitch/crest/test/api/homestead/backends/hss/gateway.py