World surface refactor

[ceeac]

Continuing from here:

simworld.cc contains too much stuff (the game loop, the map, map creation, etc)

Now simworld contains less stuff. The new surface_t base class contains all "low-level" map objects like buildings, vehicles, terrain and climates, while the "high-level" stuff like convois, cities, factories etc. stays in karte_t for now.

[prissi]

I see no obvious problems (but only did a quick check).

Not sure what the purpose of reordering the names in the MSVC project files is, because I get always an alphabetic presentation without paths. And the comilation order is also random, sometimes tarting at the end.  If there is a setting to see something else or force compile order, it is extremely well hidden ...

But that should not stop this patch.

[ceeac]

This makes editing the project file manually easier, for example to add a file to compile. Otherwise there is not a huge difference I think.

Submitted in r10536.