Add Panning ability to texture window

Sometimes I have to review the textures in UE4, and it’s really annoying to scroll them by the scrollbars and not being able to pan with RMB as in the BP editor window.
Can we have that feature?

Hi S-ed, I believe I was able to implement the feature you requested in a PR, see Cheers,

@project.gheist Thank You!

> We have accepted this commit into our Main branch, CL#14135331.