Changed UV coordinates slightly for bottom right of the icon, to not overlap the front of the skin's hand. Updating ICONS.md assets to use new UV coordinates.

Scaling all icon/skin images to 256 for clarity on tutorial, and linking to templates for downloading.

Updated README.md with new video thumbnail, and simplified text, added spoiler to install instructions

Updating README.md, renaming COPYING to LICENSE.md (replacing with markdown version of GPLv3), updating screenshots to owlmaddie versions.

- Removing example mixins (from Fabric starter project)
- Replacing old screenshots
- Added Discord invite link to README