Extract a session strategy so that cross-request storage can be pluggable. (SOCIAL-314)
SOCIAL-416 Reimplement Implicit Grant support

- Remove deprecation notes
- Add tests back
- Add comments about using Implicit Grant as last resort
Merge pull request #125 from royclarkson/SOCIAL-416

SOCIAL-416 Reimplement Implicit Grant support
Combined non-static ProviderSignInUtil methods into ProviderSignInUtils. SOCIAL-314
Merge branch 'session-decouple'
Build reference docs from asciidoc. SOCIAL-410
Construct RestTemplate with a culled set of message converters. SOCIAL-423
Adjust dependency versions
More edits to reference docs.