Added Experience, ranks

Added Player Trait PlayerExperience, added Actor trait GivesPlayerExperience.
No GUI yet, but the first basics are there. First step for #6154.
![image](https://cloud.githubusercontent.com/assets/7933210/3902515/e80f08e8-22be-11e4-898b-ccff1831c0df.png)
MS Vusual Studio is giving error.