EarthManipulator::_findNodeTraversalMask and related setter/getter methods

Added _findNodeTraversalMask and proper setter / getter methods to change/read mask used by manipulator in internal find node traversals looking for root MapNode and CoordinateSystemNode.
Manipulator functionality is crippled when these nodes cannot be found. So use this variable and these methods when you change MapNode or CoordinateSystemNode masks. 
Default mask is set to 0x1.