-Feature: reserve cargo for loading vehicles in distinct lists and thus don't recount it in every loading round

Conflicts:

	src/saveload/saveload.cpp
	src/saveload/saveload.h
-Fix: cleanup
-Codechange: start implementing unload sorting
-Codechange: further work
-Codechange: more work
-Codechange: Finish the load action stuff
-Codechange: more stuff
-Codechange: move things around some more
-Fix: some silly bugs
-Add: some documentation