Created Grid Class

Made a Grid class that stores a character for each coordinate.  You can
draw the grid, get a specific coordinate, and set a specific coordinate.
Added Aircraft Base Class, Cleaned up placeholders

Fighter now inherits from Aircraft, got rid of some of its functions for
now so they can be re-implemented.  Spy Satellite and Bomber also
inherit from Aircraft.  Re-formatted some of the classes to keep things
clean and consistent.