Fix some more lint warnings

see commit message for details!

also suppressed warnings from update to Android sdk 18 (currently 14 new warnings in Eclipse after update target sdk)

lint warnings current master branch: https://jenkins.catrob.at/view/Util/job/Catroid-Code-Checker-master/18/androidLintResult/?
lint warnings this branch: https://jenkins.catrob.at/view/Util/job/Catroid-Code-Checker/57/androidLintResult/?