Add subscription-state header
Merge branch 'dev' of github.com:Metaswitch/sprout into iss505
Add comment
Add separate sub state parameter
Merge branch 'dev' of github.com:Metaswitch/sprout into iss505
Merge branch 'dev' of github.com:Metaswitch/sprout into iss505
Merge branch 'dev' of github.com:Metaswitch/sprout into iss505
Merge branch 'dev' of github.com:Metaswitch/sprout into iss505
Change to enum classes
Merge pull request #650 from Metaswitch/iss505

[Reviewer: Rob] Iss505