Add HDRP/LWRP support

[AndrewRH]

Currently the ApplyToMaterial/ApplyToMesh scripts don't work correctly. This is due to materina.mainTexture not working with HDRP, so it needs to be changed eg:

				//_material.mainTexture = texture;
				_material.SetTexture("_BaseColorMap", texture);

Have to see if anything else needs changing too.

[AndrewRH]

Another part about supporting HDRP that is difficult is alpha for External Keying, since HDRP doesn't support rendering to alpha channel....

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[krisrok]

just to clarify: is (or was) this just a tooling problem? i guess we can still manually apply the texture for it to work with the SRP-implementations? it's just texture data after all..