Implement GM_setClipboard

[sumanth-culli]

This should be comparatively easier than other GM APIs.
Possible implementation : https://techoverflow.net/2018/03/30/copying-strings-to-the-clipboard-using-pure-javascript/

[quoid]

@sumanth-98-dev I will look into adding this in the next feature push

[quoid]

done in v4.1.0, v1.1.0