Reenable signals/slots for camera update redraws

This should enable the camera to be easily controlled from outside of
PointView, with any required redraws occurring automatically.  Use
update() rather than updateGL() in restartRender() to avoid a mysterious
crash.  This also makes more sense in some ways, since updateGL() forces
an immediate update which may conflict with other events in the event
queue.
Camera automation via socket interface

Define a socket interface message SET_VIEW_ANGLES which can be used to
set the view in the 3D window to a given yaw, pitch, roll.  (issue #27)