Modified tree generation and sapling growth calls

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* Deleted some outdated textures.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.