Modified interactor style: display camera parameters

This is a more user friendly way to display camera info when the user presses "C" in the viewer. It also changes the way .cam files are written when pressing "J".

Example of new output :

Clipping plane: [near, far]	0.605189, 5.31035
Focal point: [x,y,z]	0, 0, 0
Position: [x,y,z]	-0.77742, 0.395603, -2.23865
View (see doc) [x,y,z]	0.11999, -0.969652, -0.213021
Camera view angle:	0.523599 rad
Window size: [x,y]	960, 540
Window position: [x,y]	903, 249