Fix modules for name-retrieval functions in utils.
Update to use new units constants.

- Change units attributes to use constants instead of strings.
- EPR/TPR are ratios and have no units - be explicit - use None.
- Eng Vib parameters have no units - be explicit - use None.
- Mach-related KPVs should have 'Mach' as a unit, not 'kt'...
- Duration KPVs should always be in seconds... Not percent!
- Added in many missing units to derived parameters and KPVs.
- Move units, etc. to the top of the class definitions for clarity.
- Resolve inconsistencies between units in different modules.
- Fix some dependency parameters:
  - 'Speedbrake Handle (*)' should use P() not M().
  - 'Stable Approach' should use M() not P().
- Also tidy some docstrings - used to populate database.
- Make use of all_of and any_of is some more can_operate methods.
- Add some comments regarding possible code improvements.
Correct the units for engine oil quantity KPVs.