Adopting PrettyGCode plugin

[jacopotediosi]

• You have read the "Registering a new Plugin" guide.
• You want to and are able to maintain the plugin you are registering, long-term.
• You understand why the plugin you are registering works.
• You have read and acknowledge the Code of Conduct.

I've finally completed the work needed to adopt the PrettyGCode plugin.

As shown in the changelog of release 2.0.0, this involved 20 very intensive days of work, which included a massive refactor and the fix of numerous bugs. Overall it amounts to a difference of +10k -9k lines of code, but I'm finally satisfied with the new state of the frontend code, which I now find particularly robust and readable.

This adoption request closes the long-standing #1342 (close #1342).

[jacopotediosi]

To make the review easier: previous maintainer/repo references within the plugin code have been replaced by this commit

[jneilliii]

To make the review easier: previous maintainer/repo references within the plugin code have been replaced by this commit

and apparently lots of fixes afterwards...

[jacopotediosi]

Thanks for merging Jim! ❤️