Create pitch/roll control for skymaps

[Peregrine05]

Currently, the only rotation control for skymaps is yaw. But pitch/roll control would be useful for some skymaps. For example, the Milky Way Panorama by ESO is a full 360x180 skymap. The skymap can be rotated on the yaw axis, but the Milky Way will always be on the horizon. In real life, that is not the case; it runs up and down through the sky. If a pitch/roll control existed, the skymap could be positioned in any way you like. So, a pitch/roll control for the skymap in addition to the yaw control would be useful.