Add Galaxy skeleton
erltrek_galaxy: add initial state.
erltrek_galaxy: spawn klingon ships.
erltrek_galaxy: add ship defs.

The ship defs holds specs for the ship, such as max energy capacity etc.
Currently there is nothing much in them, but more will be added
as new features are introduced.
erltrek_galaxy: add spawn_ship/1.
erltrek_galaxy: monitor ships, notify when they die.