Scarecrow now a proper golem.

Now scary to all non-golems. Except spiders and endermen, because they're even scarier.
Other golems, of course, know no fear.

Also, are no longer pushed around or collided with. Or take fall damage, for that matter, due to their new golem heritage.

Would like to still improve responsiveness, target selection.
Merge pull request #275 from bolte-17/scarecrow

Further scarecrow improvements