Item inspector

[FaceDeer]

I use this all the time while developing my own mods and it's awesome. But I've been doing a lot of work with craft items and tools that have metadata lately, and this didn't handle those. So I added a formspec for inspecting items in my inventory. Use "/inspect_item" to bring it up.

While I was in here I also made a few other changes that I hope are all reasonable "cleanup" style tweaks, if any of them are unwelcome let me know and I'll retract this pull request and offer one without them. To wit:

• I made the fsc dependency optional. I usually develop mods on a very bare-bones world without other mods installed so I'd rather not have to include fsc just for this, and since there's no on_receive_fields method to secure in the first place I'm not sure there's much benefit to be had anyway.

• Added the LGPLv2.1 license text explicitly to the repository.

• Also, wrote up a simple README.

• Optimized the PNGs, because why not.

[FaceDeer]

I just added a quick bugfix to this pull, inspector was crashing when you tried inspecting an undefined node.

[SmallJoker]

Will merge after the comments are handled and the PR re-tested.

[FaceDeer]

There were a bunch of other similarly squashed ifs and fors, I expanded those too. I left this group alone, though, it seemed more elegant in its current form.