Clarify that banking does not tilt the coordinate system

[HeyImJordi]

One of the images on banking in the OpenCRG 1.2 spec suggests that the uv coordinate system is tilted when banking is used. During discussion with 3D Mapping and @nicco.dillmann it was agreed that the image is wrong. It should be corrected in the next version of the standard.

[3Dbastian]

the Figure should be corrected in that way:

or directly rename x to v ?

@asadekasam
Is the original vector-drawing available at ASAM, so it can be modified? Since in the repo only the raster image exists I think (doc/specification/images/banking_slope.png)