Scene loader

[Bartanakin]

Now, all the scene configuration remain at the Sandbox constructor body. Every time a new test configuration is required the previous one is commented. In this issue we want to add a mechanism that stores all the scene configurations and loads each by one call.

Best if the call was compilation-independent, I mean there is a parameter in the program execution line that tells which configuration is to be applied during generation of the scene.

EDIT
After merging #44 we want to select different scenes without any recompilation. So the input in the execution line should be the scene's file name from BartaEngineSandbox/scenes.