This fence gate builds on NDT_CONNECTED by assuming fence nodes will
automatically connect to it's sides properly. The fence gate will
open and close just like doors, with sounds, but it only opens one
way. The gate sticks out quite a bit and can be bumped into, so the
fence may be used as some sort of path switch.

The fence gate offers no form of protection and can be opened and
closed by anyone. This is done on purpose - the fencegate isn't
meant to provide protection from players, as fences can be
trivially jumped over. Instead, these fences should be used for
protecting crops from hungry sheep, or keeping rabbits in their
pen, or just decoration. Mods can also modify the mod to add
protection, of course.

A recipe is added to make these. It's 4 sticks and 2 wood (any)
as follows:

  stick  wood  stick
  stick  wood  stick

The collision box of the open gate is such that if two gates are
connected but mirrored (making an M shape) then you can walk a large
entity that's larger than 1.0 wide through the opening. The gate of
an opened fence can also be stood upon or bumped into.

I've mixed together some sounds to provide a somewhat light sound
experience, one that one would expect from a small gate latching open
and close.

This change requires #873, otherwise it doesn't connect to fences.