Update licenses to my textures

[Askaniy]

Most of my textures were switched from CC-BY-SA to CC-BY.
Also indicated that Uranus hasn't free license.

[pedro-fixingstuff]

The original authors of the assets used in those textures should be attributed. For instance, most of them are based on maps by Björn Jónsson, and the Phobos texture is based on maps by Philip Stooke.

(although whether this should go further and also attribute the agencies which provided the imaging instruments for spacecraft is another question)

[Askaniy]

If we could link to DA or Flickr, that would solve all the problems. Constructing credit chains manually would take a lot of effort and there is uncertainty.

[ajtribick]

I'm in agreement with @pedro-fixingstuff - we should have the credit lines for Björn Jónsson / Philip Stooke here