Adaptation of SDL tests in SDL C++ layer

[asmodehn]

The goal is to have the same test than SDL in the SDL C++ wrapper.
So all the tests should be ported and adapted to the wrapper, one by one.
This will be very helpful to debug problems that start to arise without having to go through a big test application.
We could also this way compare results easily.

[asmodehn]

We should be able to slowly make the required changes, but keep the tests working, as we can continue to use the raw SDL calls until the C++ wrapper of it is implemented.

[asmodehn]

Postponed, just because we need to have the tankgame working asap, and the library is quite ok now... We will port the test later.

[asmodehn]

Need to implement a structured set of tests to be able to say which part of the library works and which doesnt. Without that, it s really hard for users to work with it...