Free up all alphaumeric keys for user keymapping

[TubularCorpration]

OK last suggestion for a while, but since it came up in the other thread I think it would be a good idea to move all of the hard-coded functions (mostly in the dev branch) to non alphanumeric keys, and open up access to a-z and 0-9 for mapping functions to. It would make using larger keypads straightforward, and there would still be plenty of keys left over for the hard-coded stuff that's mapped to letters right now. At the very least you'd still have 11 keys free just in the standard English character set: `[];',./-=``

I mentioned it in passing in a different thread, but I modified numpad_input.py in my 2.10 install already:

` def on_key_press(self, event):

numpad = list(string.ascii_lowercase + string.digits[0:36])

if event.char is '.':

    self.actions.quit_the_program()

elif event.char in numpad:

    self.run_action_for_mapped_key(event.char)

else:

    print('{} is not in keypad map'.format(event.char))`

` def on_key_release(self, event):

    numpad = list(string.ascii_lowercase + string.digits[0:36])

    if event.char in numpad:

        self.check_key_release_settings(event.char)`

That works, but it makes updating more complicated, especially if/when the changes to those functions that have already been made in the dev branch get added to the main branch, so having it formally added would be great for me (and anyone else down the road who wants to use a bigger USB keypad).