Fix issue#54.

Wrong median position calculation for bricks produces negative list index.
Add robotium test for issue#54.
Fixed failed ui tests caused by fixing issue#54.
Merge branch 'master' into issue#54
Merge branch 'master' into issue#54
Merge branch 'master' into issue#54
Merge branch 'master' into issue#54
Merge branch 'master' into issue#54
Add issue link to testcase.
Refactor variable name.
Merge pull request #142 from Catrobat/issue#54

Issue#54