Created Trade Screen and implemented some functionality
Pulled from master, these are the changes made
Merge branch 'master' of https://github.com/Rrego6/space_traders into ivan

Conflicts:
	SpaceTrader/res/css/WelcomeScreen.css
	SpaceTrader/src/controller/PlanetDrawScreenController.java
	SpaceTrader/src/helper/CommonHelper.java
	SpaceTrader/src/model/Inventory.java
	SpaceTrader/src/model/Planet.java
	SpaceTrader/src/model/TradeGood.java