[GSoC] UserBricks Branch

Since it's the GSoC "soft deadline" today I decided to start this pull request. 

If you don't already know, this was my GSoC project: to implement custom bricks in Catroid, similar to user-defined functions in a programming language. I'm not sure if I should submit the pull request like this, with one commit, or with all of my 180 commits from the summer.

There are some documentation files about the project collected in a google drive folder here: https://drive.google.com/folderview?id=0B1qnfN89gHX7eWRobmREbHhiMVE&usp=sharing

Also, if you are on JIRA, this is my agile board: https://jira.catrob.at/secure/RapidBoard.jspa?rapidView=17

I achieved my goals, but I was unable to go beyond them and implement some extra goodies that I'd planned in case I had extra time.

This branch is not necessarily ready to merge into master: I still have some work to do.

Problems with the main program:
   • I left "CHANGEME" strings in the values-de/strings.xml file.

Problems with the tests:
   • We should do some more user experience testing, to troll for edge cases that can cause problems

Problems solved since starting the pull request:
   • Fixed bug where On Start would be added to user bricks sometimes.
   • Fixed cycles in UserBrick call order causing force closes.
   • Some of the user bricks tests are pretty sparse, some more things could be tested. 
   • Needs ability to delete user bricks.
   • Bug in my placholder graphics.
   • I'm not getting checkstyle errors, but some things might not be up to the coding standards.

I'm starting a Catroid-Multi-Job-Custom-Branch Jenkins job on this branch, it should be here when it's done: https://jenkins.catrob.at/job/Catroid-Multi-Job-Custom-Branch/445/

I expect it to run with 0 failures, but we'll see ;)