First person camera, fixes #1295

The new camera can be activated through the artist menu (where all camera related items were moved to a submenu).
It's possible to move with WASD keys and rotate with Q and E. This only works if no keyboard configuration uses that keys (see #1715). The mouse is used to change the camera direction and the scroll wheel changes the movement speed. Pressing ESC returns to the normal camera.
There's also a smooth mode which tries to make the camera movement smoother.