Adding The Prince and the Coward

This pull request is about Prince engine, which allows to handle “The Prince and the Coward” game. (http://www.mobygames.com/game/prince-and-the-coward)

The engine is developed by john_doe, malik and me. All my work was done during the GSoC 2014 project (http://lukaslwgsoc.blogspot.com/).

The game is completable in Polish, but still lacks English translation (I’m going to start working on it now.)

List of TODO’s:

•	Play-through the German version
•	Test game on big-endian machine
•	Handle sound and music settings
•	Throw a rock mini-game – sometimes after finishing a mini-game, during the last animations, bird appears in 2 places (probably glitch in script)
•	Several glitches with drawing shadows may appear (need testing)
•	Pathfinding  - in map location, after spam clicking on unexplored location, hero can stuck and start repeating over and over: “I’d better return to known territories…”. 
•	Allow intro skipping
•	Support loading during game start-up
•	One-armed bandit mini-game - last row of skulls can be bugged if we pull the lever immediately after pressing the button third time (while the last row still slowly rotate). Bug also appears in original version of game and it doesn’t break whole mini-game.
•	Bad colours of inventory’s background in „Before Fjord Castle” location. Bug also appears in original version of game.
•	Broken animation of disguised woman (after giving her the poison) in Tavern location. Bug also appears in original version of game.

Please help with code reviewing, every comment is welcome.

Seems a bit inconsistent with the nullptr usage used elsewhere, perhaps use nullptr in this file too?