Added baron selection, additional buildable tile types, and more!

* Added a baron selection screen at the beginning of the game. Each of these grants a unique buildable tile and additional bonuses based on your selection to offer more variance in playstyle.

* Updated a lot of balancing so that trains receive more of a bonus from upgrades. More trains, more fun.

* Updated the market panel so that it's always open. User feedback indicated that people wanted to be able to watch prices more easily.