Sc 107/default extention file selection

What's new:

• Automatically goes to the correct dir, depending if you look for shadows or source files!
• Has .csv as default instead of .txt
• Added .TextGrid as option
• Title of file selection window dependent on whether you look for source or shadow files
• File selection function has no code duplication anymore
• Layout of code in some other files is fixed to meet PEP standards