(svn r15541) -Revert (r15399): 'v->cargo_type' is also used in other places, which cannot accept CT_INVALID.
-Codechange: Add Engine::GetDefaultCargoType() and Engine::CanCarryCargo() and use them.
-Fix [FS#2617]: When articulated parts have no available default cargo, use the cargo type of the first part for livery selection.
-Change: To decide whether a vehicle is refittable do not test its current capacity for being zero, but always use the 'capacity property'.
Note: The property is used unmodifed without calling CB 15/36. By setting it to a non-zero value and returning zero in the callback vehicles can be refitted to/from zero capacity for e.g. livery effects.
Note: It is intentional that you cannot control refittability by CB 36.

(svn r14683) -Change: only say a engine/vehicle is refittable when it can be refitted to at least two cargo type or when it has subcargos.
NOTE: it is still possible that a vehicle is marked refittable when there is nothing to refit to, e.g. when only one subcargo is available but that cannot be determined without a vehicle chain.

(svn r13887) -Codechange: Replace numbers with Colours enum on autoreplace, build_vehicle, cheat, depot and dock guis.
The fact that it goes alphabetically is pure coincidence.

(svn r13696) -Fix[GUI]: The Build button of the vehicle list is now hidden, instead of just disabled. It will be only visible when called from the Depot Building Window.
Less confusion, hopefully. Suggested by Eddi.

(svn r13251) -Codechange: rename _patches to _settings as that is more logic.
-Codechange: move all Settings into substructs of _settings in a way that they are logically grouped.