* Added various views and helper functions used by the mining
computation but which may be re-used in other parts.
* Added mining computation update type and associated update function
* New constants: game.resources.weightBase (the value used to compute
weights from mining settings) and game.resources.extraction (the
quantity extracted in a day from a full provider at difficulty 0)
* Added a new update that computes the amount of resources possessed and
owed by empires. At the moment this computation ignores fleets, as their
upkeep does not use the resource system.
* 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
