Massive changes how all units are used.
Uses a hash to store all units.
Some cleen up of the code structure.
Simplified the graphictask.
GraphicTasks is now drawn in correct order.
Fixed consistent code layout.
The human can now go in and out of cars.

The action key 'e' is used to go in and out.

A problem however is that the physics of the car is not updated when the
car is empty. The cars can therefore easily bee moved around by pushes.
The human can now take up new weapon.

That is the blue dots.
Cars whitout driver has have wheel friction.
Added new sky class.

Sky class is supposed to show clouds above the map. And perhaps simulate
different kind of weather conditions, e.g. rain.
Using CMake

Git submodule add MwLibrary, MwExtra.

External library Box2D is used and all the code is copied and used as a
subproject.
All data files is now copied to the build folder during execution of CMake. All data files are moved to the data directory.

For windows, all dependent dll files are included in the dll directory.

Updated readme file.