Update command sketch to work on the Embedded Artists panel.

Most of the changes are #ifdef'd, though not quite all.

This is based on the flash_loader_epd_ea sketch's changes. I started factoring out the SSEL
management, but more clean-up is still possible there.
Merge pull request #1 from kcarnold/master

Update command sketch to work on the Embedded Artists panel.

Thanks @kcarnold -- looks good.

>> I started factoring out the SSEL management, but more clean-up is still possible there.
I didn't refactor like this mainly to be able to make it easier to take any upstream changes without clashes to this partial screen version.  I didn't try to push upstream as I believe the partial screen support changes impact enough things to warrant a fork -- happy to think about requesting a pull up though.