Apply `ENABLED` / `DISABLED` macros to files needing only a small
number of changes.

Makes the output on the LCD adjustable.

With these changes the output of `M503 S0` is all you need to restore
the EEPROM. Building on this it is straightforward to save and restore
the EEPROM state using the SD card or external GCode file.

- Added `M145` to set “heatup states” for the LCD menu
- Added `M420` to toggle Mesh Bed Leveling
- Added `M421` to set a single Mesh coordinate
- Extended `Config_PrintSettings` with added M codes
- Cleaned up some comments here and there

Better explain the watchdog "problem" and rename the config define so it explains that the feature belongs to the watchdog.

First cleanup. Moved all code to cpp files, so there are no dependencies on pde files. And no more odd requirement to cat files together. (Still need to fix the Makefile). Also cleaned up some defines and made defines upper case as by C coding conventions.