Subject OPTIONS requests to overload controls and add deadlock detection for worker threads
Application service interface - initial version
Mark-ups to AS interface
Enhance UTs to catch missing Subscription-State and Allow-Events headers
Add missing Subscription-State and Allow-Events headers
Fix respond_stateless bug - don't skip the first header
Improve comments
Reverting Subscription-State header
UT framework and interface mark-ups
Mark-ups following interface review.
Fix Doxygen
Move to latest cpp-common
Merge pull request #643 from Metaswitch/subscription_headers

[Reviewer: Ellie] Subscription headers
Use abort() instead of exit(1) when deadlock detected
Merge branch 'dev' of github.com:Metaswitch/sprout into iss630
Code review mark-ups
Merge pull request #649 from Metaswitch/iss630

[Reviewer Matt] Subject OPTIONs to overload controls
Further code review mark-ups - add free_msg API
Merge pull request #646 from Metaswitch/appserver

[Reviewer: Mike] Application server interface and UT
Pull latest cpp-common