Added player with left/right movement, refactored

Basic player texture added, just uses the "standing" animation to draw.
Need to install more sophisiticated tools before I can make the texture
background transparent.

Also refactored some code. Biggest change was that I moved all of the
keyboard input handling for the Main Menu screen into the MenuComponent
class. It just seemed weird to have half of the keyboard logic in the
MenuComponent (up/down) and half in the main Game1 class (enter). Used a
similar approach for the ActionScreen.