Code cleanups: units map, more obvious subdirectories in engine, automatically checke

[DP News-Robot]

Lately I’ve done a number of rearrangements in CGE units, to make the engine code cleaner (easier to understand, both for new people and seasoned devs): Units map documentation is now up-to-date and more straightforward. Unit dependencies outlined in units map are (again) automatically checked by check_units_dependencies internal tool (using ppudump from FPC underneath). A …