Add support for CurseForge provider

[sorae42]

This one is kinda hard since they don't have a public API to work with, even if they did, sometimes mods won't allow downloading from external sources, which make CargoDrop just not working.

[sorae42]

It seems they do allow downloading directly from CDN (literally not even walled!). However, generating sources using CurseForge is not feasible as they requires an API key.

I think for now I'm not gonna work on this and just gonna plug direct URL manually.