Fix a crash when IntegerRenderer is passed a null value
UI tweaks to rules window
Additional UI fixes to rules window

    - Use cell renderer centering to fix various cases where checkboxes
      appeared in the wrong place
    - Use a dummy scrollpane instead of a border for state-qualifier
      table to fix a mystifying case where clicking a checkbox clipped
      the border
    - Add OTable, which is a JTable subclass that hides the
      cell-selection highlight (this may be a Mac only issue)