add changelog file
Clean up catroid projects

Remove unnecessary casts
Organize imports
Format code
Convert for into for-each loops
Merge pull request #816 from Catrobat/addChangelog

add changelog.txt
Merge pull request #817 from Catrobat/cleanUpProjects

Clean up catroid projects
rewrite changelog to markdown
Merge pull request #818 from Catrobat/rewriteChangelogToMd

Rewrite changelog to Markdown
Merge with master + conflict resolve