Start angle for motion-based panoramas

[Sega-Zero]

This PR provides ability to specify start angle for motion based panoramas as well as touch based.
I also would like to apply start angle to sphere panoramas too, but couldn't figure out where should I apply it.

[scihant]

Thanks for the PR. Applying the starting angle in the spherical case is much harder because you need to calculate a new quaternion that has only one of its axes modified.

I'm merging this one for now but I think that modifying the texture coordinates of the geometry could be a better solution for this because it could work both in cylindrical and spherical cases. I'll experiment with the idea when I find the time. Feel free to try it yourself to see whether it would work.

[Sega-Zero]

I was hoping the same y-axis patch will work (and it's actually what I really need now), but couldn't get it working :) Unfortunately, I don't have enough knowledge in this area, so I would be very appreciated of you point me to the right direction :)
I need to start a panorama at specified y-axis location and then rotate it when user moves a phone.