Continuation of @wow4201's Item Frames

This is a continuation of Item Frames support, started by @wow4201.

I've made some checkstyle fixes, and prevented item from being removed from a player inventory in Creative.

Glowkit: https://github.com/GlowstoneMC/Glowkit/pull/52

@wow4201: If you decide to pick this up again, I'll close this PR and give all the code to you.
Also I just realized turt2live probably meant that the if (player != null) should probably end right before this `metadata.set` line