Housekeeping.
Add test case for Command Centers.
Add command center isk_cost, pg usage and cpu usage tests.
Split command center increase level and decrease level tests out into two.
Add launchpad tests.
Remove unnecessary setters from CommandCenter.
Add ArgumentError when someone tries to set a level outside the bounds.
Fix bug where CommandCenter would notify a change even if the upgrade level did not change.
Add "should not" tests for "Observable" behaviour.
Add test for storage facilities.
Use assert_true() and assert_false() instead of assert() and assert_equal(false, ...)
Add initial basic_industrial_facility test.
To make copy-pasting easier, set all building tests to use @building.
Add default startup and shutdown methods.
Add comments for setup and teardown methods.
Add a test suite for all the model tests.