Create demo application

[Witek902]

The current nfEngineTest application is very limited (it shows only a few engine's features). The demo should have mulitple switchable scenes that present different features. The demo should be written cleany and be well documented (it will be the reference point of game developers).

The demo will also be a high level testing utility (after making a commit one will be able to verify the change by playing with the demo and checking "if it works OK").

[lookeypl]

To make this task possible, we need full list of engine features which we want to use in such demo. Maybe such list should be split into scenes (some demo scenarios?). I suggest to move this task as a proposal right now, since we need to discuss it and gather all the info needed.