Implemented the SphereSensor node with "rotation_changed" event output.
The SphereSensor node maps pointing device motion into spherical rotation about
the origin of the local coordinate system.
Added the Screengroup node of the Layout package.
Merge pull request #376 from ankit1089/sphere_sensor

Implemented the SphereSensor node with "rotation_changed" event output.
Added regression tests for the Screengroup node.
interact/navigate: check for enabled state of pointing device sensors
Merge pull request #377 from girier-tsha/layout_component

Layout component