Imports cleanups

Removing some unused imports that were in the wrong files.
Squishy slimes

Slimes now spawn in the green swamp, using the same rules as vanilla
swamps, sans the restriction that the biome must be a vanilla swamp.
Scarecrow Fix from conflict with Artifact

Don't register the scarecrow globally, only register it as a mod entity
and not globally.
Fence issues

Fences and fence gates did not have hardness set so they were breaking
instantly.

Fences did not override the default dropped block metadata.
Merge remote-tracking branch 'remotes/github/master' into develop
Added 1.7 food hook support to raw crops (github #404).