Updates plugin for 3.2.1

[loicSketchfab]

A few minor changes to make the plugin compatible with the most recent versions of Godot.

[loicSketchfab]

Still need to update the docs, in particular, move the installation / usage instructions to the README.md as was done on Blender and C4D plugins.

[loicSketchfab]

Updated the docs and fixed icon handling. Will need some testing on Windows (linux only so far), but other than that, should be ready to go !

[noidexe]

Working fine! I tried:

• logging in
• searching for an asset by name
• downloading an asset
• instancing the imported asset

It took a while since the import finished till the editor responded again but that's an issue with the Godot importer not the plugin.

Please merge it since everyone downloading from the asset library thinks the plugin has been abandoned.