Fix glowstone drops and add config for chance

I'm baaaack.

Turns out glowstone drops were bugged. 

It was still based on the actual block's meta so sometimes magic ones dropped and sometimes regular ones didn't.

Now there's a config option. By default the chance is 1 out of 3 per side. This means that if 3 sides are illuminated, the drop rate for 1 glowstone is 100%. If 4 sides are illuminated, the drop rate for 1 glowstone is 100% and for 2 glowstone is 33%. The config option has the exact math in its comment. The max for the config is 2.0, meaning each side guarantees a drop of 2 glowstone, meaning you always get all of your glowstone back, but it can't go higher to avoid dupes.

Also fixed a small issue where the arrow would "replace" magic illuminated sides with regular ones.