Plus Radius can now be cast on its own

[SoulMuncher]

closes #762

Which lets players increase Urn Radius without needing another spell

TODO

• Is there a clean way to improve refund logic? (I.E. should [Plus Radius + Slash] refund plus radius since it has no effect on the spell?)
• Done otherwise

[jdoleary]

Is there a clean way to improve refund logic? (I.E. should [Plus Radius + Slash] refund plus radius since it has no effect on the spell?)

I say this is on the player, if they use it with no effect then they'll just have to learn