Fix T38654: Using a non-camera object for the SetCamera Scene Actuator causes a segfault.

Non-camera objects are not supported as cameras, and trying to use them
just causes memory errors (some bad typecasts are involved). When converting
a Scene Actuator, only use the object as a camera if it is actually a camera.
Also, the logic brick UI now filters for camera objects, which should help
avoid confusion.
NDOF: use like a joystick for cube picker (as with circle picker)
NDOF: image and clip views ignored axis invert preferences

also X/Y invert was swapped for 3d view.
NDOF: fix for broken zoom invert for image and clip editor

also match zoom speed with 3d view
NDOF: show invert pan & zoom in the menu outside the 3d view
NDOF: support pan/zoom for view2d (nodes, graph editor, sequencer... etc)
NDOF: add keymapping for the 'fit' button for other 2d views
Fix FCurve reading freed themes, assert to prevent further misuse