Implement basic ShipFactory to construct ships

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Make ShipFactory produce multiple ships in one call

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Add cost variable to ships

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Add planet as specialised GalacticObject

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Allow agent to select the last suggested target object

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Prevent out of range index on GalacticObjectScreen

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Add Nebulas

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Clean up random value generation in tests

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Add asteroid fields

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Add GalacticObjectFactory

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Fix warnings

Signed-off-by: James Tasker <james_tasker1@hotmail.com>
Add credits and minerals as specific resources

Signed-off-by: James Tasker <james_tasker1@hotmail.com>