Added Traderable interface to Transactions.
Players can now trade with Traders encountered in space.
Merge branch 'master' into sam/dev.

Conflicts:
	src/main/java/edu/gatech/gem5/game/controllers/DisplayUniverseController.java
	src/main/java/edu/gatech/gem5/game/controllers/EncounterController.java
Implemented a new way to go to planets with a gridpane overlay. It's really ugly so far though.
Merging with master while developing planetment selection
Merge branch 'master' into jack/dev
Made everything in the universe more reachable by all of the ships. Also moved the method beginNewGame to LastAdventures because it belongs there.
Planets displaying on the universe screen is now fully functional, albeit a little ugly.
Universes' Solar Systems are now stored in a Map instead of a List, and as a result SaveFile keeps track of the current System's name it no longer needs the x/y coordinates anymore, but they are still available.
Player starts near the center of the universe again, which had been impossible since the move from List to Map for storing the universe's systems.
Character create screen keeps it's structure even if name isn't inputted.
last commit before pull from master.
Merge branch 'master' of https://github.com/gem-5/last-adventures into sam/dev
Traders now spawn with inventory goods that they can trade to the player.
Fixed UI bug, where trading with Trader was labelled as Planet.
Added trader.fxml file for TraderController
Bigger and better universes are here! Enjoy full panning and zooming action with incredible life-like immersion!
Some enhancements to the new universe display.
Major style update. Also added new star types to solar systems - update your save files!
Created ShipyardController, edited UpgradeBar so that ships can be sold.