[IDEA] Intergrate tiddlywiki's plugin installer to using tm-http-request

[Leilei332]

The tm-http-request message can be used to make HTTP requests. I think it would be better for the add plugin modal to make use of this feature.

[Jermolene]

Hi @Leilei332 the plugin library was originally implemented before GitHub Pages started supporting CORS. We probably could switch to xmlhttprequest now, but I wouldn't see much reason to change things unless we were also planning some functional improvements.