Updating FileEditor operations and Undo (see description)

* Created simple Id3Data class to use in an ArrayList for passing
Id3data to the FileEditor
* Updated Undo class to handle multiple and single value operations.
* Updated FileEditor to:
* - write edits back to MyMusic.xml file
* - Set and get app Settings (experimental)
* -- MUST use Settings enums as keys when sending Map values to
FileEditor
* - Framework for editing Id3 tags of actual files (not operational)
* -- I'm afraid we'll need an external library to edit ID3 data since
Android doesn't seem to support this function natively.
* - Framework for moving and renaming files (not operational)