Mobile "control pad"

This PR will add a "control pad" for mobile users. It can be enabled and remapped in the config file, but by default it will use WASD and enter.

There are 5 "zones" on the control pad:
The top - presses key _conf.ctrlPad.top ("w" by default)
The bottom- presses key _conf.ctrlPad.bottom ("s" by default)
The left - presses key _conf.ctrlPad.left ("a" by default)
The right - presses key _conf.ctrlPad.right ("d" by default)
The center - presses key _conf.ctrlPad.center ("return" by default)

This is one of my first times using LOVE, so I'm not very good and the code may be messy, but here's a screenshot :P
![y u no see screenshot](http://upimg.me/51d5f1b7bc6f073cbfc1aced22bbb715.png)

I plan on adding coloring/marking to the circle so its easier to tell what's what, but try it out and see what you think. I recommend trying it in worm.