bug 922006 - [camera] Support camera.sensorAngle

* Calculate dimension after rotation (a.k.a. bonding box dimension) by trigonometric functions to support every rotation angles (including minus degree). 
* Move transform center of viewfinder to `50% 50%` to make countering the position easier.
* Calculate aspect ratio by ``Width / Height`` rather than ``Height / width`` now (since it's more common).
* Some variable name changing.

Actually we have only multiple of 90 degrees, but I think using trigonometric function is much clear here.