priority events + ofEventMarkAttended + attended and priority for ofxGui
Merge branch 'develop' into feature-priorityAttendedEvents

Conflicts:
	libs/openFrameworks/events/ofEventUtils.h
ofDelegate + ofxGui with return value
Merge branch 'develop' of github.com:openframeworks/openFrameworks into feature-priorityAttendedEvents
ofBaseApp: fix keyReleased event
Merge pull request #2015 from arturoc/feature-priorityAttendedEvents

mark events as attended