EMI: Keep camera as a rotation matrix and add Lua functions for changing it.

EMI set files use a Quaternion instead of interest and roll. This was already implemented, but this patch makes this explicit. I also maintain the camera as a matrix now to reduce the overhead of converting from a Quaternion repeatedly. This also has the benefit of making it trivial to implement the Lua functions for setting / getting the Set camera rotation, so I added those functions in the second commit.