* Added missing table that should store a planet's resources data
(income and upkeep for each type of resource).
* Modified resource definition functions and universe generator to
initialise planet resource records as well
* Heavy clean-up in resource definition function unit tests
* Empire resources will be initialised when an empire is created
* When a new resource is created through the appropriate defs.uoc_...
function, it will be added to all empires as well.
* The main loader script has been updated to generate the list of files
it needs to load automatically. As a consequence, files that contained
manually-maintained lists of scripts have been removed, and definition
directories have been renamed accordingly.
* PostgreSQL extension loading and configuration has been moved to a
separate script to be loaded automatically in the main transaction.
* Data and function definition scripts that had the -data or -functions
suffix have been renamed (the suffix is unnecessary).
* Unit tests have been reorganised to follow the definition's structure.
* Documentation has been improved
