Changed to retreive HttpContext from owin context.
- HttpContext.Current sometimes is reset to null when running in a web forms application.
- Fixes #2.
Changed all tests to run async.
- They should all have been async all the time....
Added null check for httpContext.
- Http context would be null if cookie saver is (erronously) used when not hosting on system.web.
Fix #2. Nullref occuring on web form applications.