Refactor broadcast bricks

Broadcast bricks (BroadcastBrick, BroadcastReceiverBrick, BroadcastWaitBrick) now add a new message from within the Spinner through the entry ```New...```. The Button ```New...``` is removed.

Also modified prototype views so that they show default values in Spinners (Broadcast Bricks, PointToBrick, PlaySoundBrick, SetLookBrick, User Variable Bricks) as discussed with @sjaindl.

Jenkins testrun:
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-custom-branch-test/718/

http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-jUnit-test/68/
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-UI-test/479/
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-UI-test/480/