use adafruit_anchored_group instead of sized_group

[FoamyGuy]

and add bitmap files to repo

adafruit_anchored_group has a release and open PR adding to the bundle: adafruit/Adafruit_CircuitPython_Bundle#501

[tannewt]

Please put the bmp files in a folder. That'll keep the root less program specific.

[FoamyGuy]

I Moved them into launcher_assets/ and added a default_icon which was also missing. I made a new one that uses fewer colors.

Also removed sized_group.py which isn't used any longer.

[tannewt]

Thank you!