Bugfixes:
    - attempting to import a non-sf2 as an sf2 would cause crash
    - importing large sf2 files may have caused crashes
    - Cursor wasn't moving to leaf after removing a subdivision
    - double-tapping X button on channel would cause crash
UI:
    - Note Duration control
    - changed drop down menus
    - scroll with playback
- Updated Save format and location of files to External directory 
