added catch for NullPointerException
Merge pull request #1073 from Catrobat/cat-930

[CAT-930] added catch for NullPointerException
CAT-930 #close
Implementation of bubble bricks.

* Baseclass implementation for all 4 bubble bricks.
* Say-, SayFor-, Think- and ThinkFor layouts, actions and brick implementation.
* 9-patch picture.

Bubble position on stage:
* Normalization of long bubble text.
* Raw measuring of bubble size.
* Bubble placement when object rotates.
* Replacement of bubble if it's outside of screen.