* Absorb ST7735 support into the generic ST7789 driver and rename to PicoGraphics
* Delete obsolete MicroPython modules
* Refactor PicoGraphics to inherited class for each pen type
* Refactor ST7789 and ST7735 to derive from DisplayDriver
* Allow user to set pen_type in MicroPython constructor for RGB565, RGB332, P8 and P4 modes