todo: more efficient screen display

[hyansuper]

ref: https://github.com/adafruit/Adafruit_CircuitPython_RGB_Display/blob/master/adafruit_rgb_display/rgb.py

• do image conversion work(convert to flatten list and convert 565 color) at client instead of server, so server don't need numpy installed, ref: image_to_data(), color565()
• implement block write method for efficiency, ref: _block()

[hyansuper]

done