adapt code to first checkstyle version

today we agreed on the first checkstyle rules - mostly naming conventions.
the current checkstyle config can be found here: https://github.com/Catrobat/Jenkins/blob/master/customScripts/checkstyle.xml (revision 4164a37b98)

current master branch - 110 warnings: http://jenkins.catrob.at/view/Util/job/Catroid-Code-Checker-master/9/
this branch - 0 warnings: http://jenkins.catrob.at/view/Util/job/Catroid-Code-Checker/47/

local .checkstyle project settings were added to .gitignore!

Next steps: after this pull request is merged, we will add checkstyle to the pullrequesttest, and we'll modify existing rules if needed and add additional rules step by step.