Async

Title says it all ;-)

Things that need sorting:

* Some projects are 4.5 - suggest we pull out the async demo to a sample and revert the owin sample back to 4.0
* Failing tests - need to make a call on how to fix these
* Some projects disable - test projects are disabled in some build configs so I could use the rakefile to make packages.
* Aggregate exceptions - not sure if we should default to unwrapping these before they hit user handling code?
* Need to verify that per route auth still works - might not have unwrapped the exception correctly.

Rebased off latest master.