* The universe generator has been modified to generate resource
providers. The code attempts to keep the universe balanced according to
the natural resources definitions.
Implemented resource regeneration computation in the
verse.compute_provider_regeneration() function.
Created the PLANET_RES_REGEN update type, and added the corresponding
implementation.
Added resource regeneration constants registration.
* Added defs.uoc_resources() set of functions which create or update
basic resources.
* Added defs.uoc_natural_resources() set of functions which create or
update natural resources.
