add basis for own manipulator GodManipulator for navigation.

just derive from StandardManipulator and implemented pure functions yet.
remove 'using namespace osg; using namespace osgGA;'
add primitive kind of movement.

W,A,S,D for moving (the camera) for-/backward, sideward
move commentaries from godmanipulator.cpp to godmanipulator.h
improve camera movement (W,A,S,D).

start movement when key is pressed, stop when key is released
allow diagonal movement when two keys are pressed simultaniously
merge osgTestTerrain into navigation_godmanipulator
add function which stops continousUpdate when no movement key is pressed
change default movement speed from 10 to 1 units per frame
Merge remote-tracking branch 'origin/navigation_godmanipulator' into osgTerrainTest
create multiple tiles