Emulator for developing glowbit code

[DrNeil]

While developing for the glowbit matrix 8x8 it was easier to run everything locally on a PC (Debian Linux) than push the scripts to the actual hardware.
This PR #4 contains a prototype for an emulator of the glowbit matrix8x8 class.
Very minor changes were needed for the actual glowbit.py, to cater for when the rpi_ws281x could not be imported.