Enhancements of FlxPath

- added pathAutoCenter flag to FlxObject. If false, the object will not
follow the path at its center, but instead at its origin
- added setPathNode() function to FlxObject to be able to change the
node a path is currently at
Small change to FlxPath enhancements
Removed _rect and made _point private
Forgot to remove _rect references

Now compiles fine!
FlxExtendedSprite needs _rect
Merge pull request #351 from Gama11/dev_path

Enhancements of FlxPath