Integration of all game systems

Gameplay features:
 - re-integrated space combat into the main game
 - added dangerous obstacles to the planets
 - added enemy ships to the galaxy view

Support systems:
 - implemented score tracking and health
 - implemented pulling and submitting scores through JSON

Coherency and polish:
 - planets now remember how many ores were left
 - different planet types have their own surface textures
 - added transitions between galaxy and planet modes

(missing still are sounds, and smoother space combat transitions)
Several small usability improvements