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* Deleted some outdated textures.

* combined leaves definitions back into main loop with an exception for
  jungletrees (if that one is called for, it is skipped, because leaves for
  those trees are explicitly defined later)

* Made all leaves drop saplings when dug, 1/20 chance.

* Added leafdecay radii to main tree table but disabled the use of it.  To be
  implemented in the future.  Disabled leaf decay for firs.