fix naming of variables/parameters/members/constants
fix checkstyle warnings ModifierOrder

also added .checkstyle files to .gitignore
this file is used by eclipse checkstyle plugin only for local project settings
Merge pull request #571 from Catrobat/checkstylePlayground

adapt code to first checkstyle version
Update README.md

undo changes for jenkinstest
Fix typos in Constants.java

CATROBAT_EXTENTION and RECORDING_EXTENTION changed to CATROBAT_EXTENSION and RECORDING_EXTENSION
Merge pull request #574 from Catrobat/typos@constants.java

Fix typos in Constants.java

accepted by @felly
Merge branch 'master' into issue#463_2