Rotate the display based on orientation

[jscheidtmann]

If PiFinder‘s orientation is such, that the display is tilted more than (e.g.) 45°, rotate the display accordingly, similar to landscape and portrait mode on a smartphone.

Due to the square nature of our display, this should be rather easy.
Only thing to consider is some hysteresis, so when going up and tilting left, do this at (45+2)° and when going down at (45-2)°.

This was requested at ATT.

[brickbots]

I've tested run-time rotation via the display_class.device.rotation attribute and it works well! Just need someone to link it up with the configuration (only left/right?) and altitude.