Move contents of main.py to a separate file, this simplifies updating fw - main.py does not have be updated in the cube filesystem

Make display update faster by sending all page address and data in one transfer and prepare DMA for future use

Fix a bug when power button was not read correctly after switching off the ESP command signal and switch timer in ESP config for UART IRQ

Make the EV3 color sensor calibration applicable to the EV3 color sensor

See merge request !13

This works around an unexpected crash that would happen when you run the
following code:

```
cs = <EV3 color sensor instance>
# start sensor reset
cs.start_reset()
# wait for sensor reset and return new reading
cs.reflection()
```

The cs.reflection() call would raise SensorNotReadyError with the
message "Sensor has been unplugged". However, ideally, the call should
block up to 3 seconds until the sensor has rebooted.

It seems to me that the problem is caused by the fact that immediately
after cs.start_reset() is called, cs.is_ready() will still return true.
This confuses the waiting loop in read_raw_mode() - it will think that
the sensor has unexpectedly disappeared a ~millisecond later.

This commit fixes the issue by checking for the reset condition
in the is_ready() and similar functions.

Automate updating of firmware version strings

See merge request !14

I have missed that the sensor enters the "STATE_CALIBRATE_DONE" state
after the calibration. From the reverse-engineered sources it seems to me
that in this mode, the sensor will no longer process CMD-SELECT messages.

This commit should fix this by cutting off NACKs to the sensor and
letting it reboot.