Use ivy for plugin dependencies.

Depends-On: I34d7849a75cd4c7a91e04a9dad6f8073aa5a8f61
Change-Id: I65d96f91e1eb5ed7afb43dd41cd00531d809878d
Reviewed-on: http://gerrit.dmdirc.com/2736
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Greg Holmes <greg@dmdirc.com>