adds setting callback specs, also converts old setting tests to specs
implements callbacks for settings
dry up setting specs
fire callbacks only when setting was stored sucessfully
adds a spec to test invocation of multiple callbacks
specs for the OP::Notifications based settings notifier:
* arguments to the block is a hash
* no clearing of callbacks
* no callback objects
based the settings callbacks on OP::Notifications
Merge remote-tracking branch 'origin/dev' into feature/settings_callbacks
remove most parts of api v1
fix Project#completed_percentage
Merge pull request #1125 from marutosi/finn-completed_percent

fix Project#completed_percentage
Make API authentication tests use API v2

API v1 has been removed.
Fix flash message design
Remove API v1 controllers
Add cuke
Fix success message for group membership update
Fix success message for group membership delete
Remove rsb API templates
Fix api/v2/projects/level_list
push down callback block check into OpenProject::Notifications