Add menu button to generate source code from diagram

No functionality yet
Generate .java files from diagrams

 - No content in .java files

This resolves #3, resolves #4 and resolves #5
Better handling if directories already exists
Now handles if sub already directories exists
Add unit tests to ClassCodeConverter required small refactoring to enable unit testing
Merge pull request #26 from heinzdmx/sourcecodegenerator

Generate source code from diagram