3E+ banking support

This update adds support für 3E+ banking, thanks to Wolfgang Stubig (AlNafuur on AAge).

Installation:

Download update.bin to your SD card and launch the update from the menu. Don't switch off your 2600 until the screen says "UPDATE COMPLETE".

If you have a ST-LINK/V2 programmer, you can also flash firmware.bin / firmware.hex directly.

This release identifies as R.EDWARDS 14 in the menu.