Update to Save and Instument Selection features

I implemented the save functionality which saves data on the custom
patterns in special data files. The file custom.ma holds a master list
of the names of all the patterns that have been saved. The individual
patterns are saved in files with a .mm extension and are separeted by
instrument. I added a text field for users to input the file names and
buttons for users to set the instrument pattern they want to work on.