Convert Field Scheduler over to DispatcherMapField.

Convert over the minimum amount of the scheduling infrastructure
that is needed to get DispatcherMapField to compile.
Convert MapCell Scheduler over to DispatcherMapCell.

Convert over the minimum amount of the scheduling infrastructure
that is needed to get DispatcherMapCell to compile.

This required teach DispatcherBase how to determine if it should
use id3 based scheduling for uniform grids.