Addon dependencies

[sirinsidiator]

Since more and more authors are now finally switching to move libraries out of their addons and have users install them as separate addons, it would be great if we could have some way to specify these dependencies on the addon page and have minion install them together with the addon (I wouldn't mind creating a pull request, but minion is still not on github )
A panel for authors to show which addons depend on their library would also be nice.