refactor PhysicsContact inherits from EventCustom; simplify emitting collision events
fix compile error
remove the workaround cast
Merge branch 'physics_event' of https://github.com/edwardzhou/cocos2d-x into iss3716_refactor_physicscontact

Conflicts:
	cocos/physics/CCPhysicsContact.h
issue #3716: refactor physics contact
closed #3716: edit lua support
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into iss3716_refactor_physicscontact
Merge commit 'refs/pull/5268/head' of git://github.com/cocos2d/cocos2d-x into merge5268

Conflicts:
	tests/test-javascript/tests
Merge branch 'develop' of git://github.com/cocos2d/cocos2d-x into merge5268
Merge pull request #5312 from dumganhar/merge5268

closed #3716:PhysicsContact should be inherited from EventCustom, it will simplify the logic of emitting collision events