Add support for new Replugged rewrite

[Pukimaa]

The new rewrite now uses a new system and it's not based on Powercord anymore.

This PR bumps the version to 1.3.0, adds the needed manifest.json, a package.json and a build system via Github Actions.

It also updates the license as you left the year and name blank. Feel free to change it to your liking.

I also corrected the license field in the Powercord Manifest. I didn't delete it because some people might run an older version and thus still use Powercord.

I also updated the Version in the README as well as removed the Powercord/Vizality option and added a Replugged section with an install "button".

What you need to do after the PR:

• Create a tag named something with v in front for every release (v1.3.0 should be fine for this one)
  • This triggers the workflow to build the new Replugged Theme, which is needed to automatically update Discolored inside Replugged