Modified tree generation and sapling growth calls
to comply with new plantlife API

In addition to that, there have been numerous other, smaller changes:

* Tweaked palm tree model to add coconuts

* Tweaked size of all "fruit" items (really just cones).  Rotated their images
  in inventory and wield.

* Changed descriptions of sideways trunks to "Sideways Xxxx Trunk"

* Tweaked names of jungle tree leaves to be Jungle Tree Leaves (Xxxx)

* Moved jungletree trunk, sideways trunk, sapling into nodedef loop

* Renamed trunks and trunk tops to bear "_trunk" and "_trunk_top" in their
  filenames.

* Added copies of default jungle tree trunks and tops, with naming similar to
  the above change.

* Re-arranged init.lua to put all leaves/needles definitions in one place.

* Deleted some outdated textures.