Add more source locations

[Neocky]

Add more supported source locations for plugins if possible

Possible sites:

• Bukkit
• Polymart

[Neocky]

Api for Polymart: https://polymart.org/wiki/api

[Neocky]

• Curseforge

[TechnicJelle]

Would it be possible to add support for plugins hosted on GitHub as well?
Maybe it'd just be able to download them from the release pages?
I would be okay with having to manually add the links to their repos to a configuration file or something, whereafter pluGET will keep track of it.

[jeffthejeffthejeff]

And also support for Jenkins servers would be nice, which could be replaced or added with support for custom URLs.