Allow maps to get/set Filename, Rows, and Columns. Also changed the Load method to catch and handle bad input.
Added tilename parameter for the MapEditor's GenerateBlank() method. Also removed the x,y parameters because we can just rely on the rows & columns Map variables.
Added dialog boxes to the Editor.

  Press 'a' - Save As
  Press 's' - Save
  Press 'n' - New blank map (prompts for rows & columns, defaults tiles to the currently selected tile in the tilebar)