Added configuartion option KICAD_NANOMETRIC for this.
* With option set to false: *
- it should work and compile as usual
- some values are saved with decimal point (which should be backward/forward compatible as old versions should just drop fractional part)
* With option set to true: *
- lengths in Global Design Rules should be settable 1nm steps.
FROM/TO_LEGACY_LU(_DBL) macros introduced for easy interconnection between old and new units.