Improve Void Quiver

Lots of things stacked against this item.  Off (and split) damage type, procs notably dependent on spellpower scaling.. May as well improve the payoff for somehow being high spellpower on a bow using class.  Also let it have a secondary role as an anti-armor item swap.

A redesign would probably be better.

- Increase Magic damage scaling

- Increase APR

- Improve procs