Generalize mouse input

- [x] generalized the MouseDown/MouseUp triggers to work with every MouseButton (not just left)
- [x] adjusted demos&readme accordingly to the generalization
- [x] fixed some javascript link issues in the demos/demoX.html files
- [x] renamed this._pos inside MouseFace component -> the isometric component of crafty is already using that variable name
- [x] removed unnecessary code from MouseFace component