Add feature flag for github sync

services/web/app/coffee/infrastructure/Features.coffee

@@ -8,5 +8,7 @@ module.exports = Features =
 		switch feature
 			when 'registration'
 				return not Features.externalAuthenticationSystemUsed()
+			when 'github-sync'
+				return not Settings.disableGithubSync
 			else
 				throw new Error("unknown feature: #{feature}")