Metatests on "dice.py" now work.

The tests confirm that the testing framework for dice rolls is in place. This makes
the "dice.py" function "roll_dice()" deterministic, which is a precondition for
the definition of tests for all other functions that rely on the roll of the dice
(such as the "world.py" star system generator).
Continued with the tests of world.py

Added all checks except for the factions, the bases and the trade codes.
These are more complex (objects in objects) and will be added later,
together with the shell script needed to run the tests (setting
PYTHONPATH so that the dice functionality is found).
Test infrastructure established.

Tests in place, world.py now covered. Tests do NOT run green yet! There
is a runtime error in world.py.
Tests run now green.

Test framework is in place, world.py runs green, tests in world.py have
been made more robust in case of wrong arrays (only access them if the
number of entries has been verified successfully, thus avoiding
out-of-bound array errors at runtime).
Finish AddTestsToPlanetCreation