Coloring Concurrent Index Space Task Launches

This branch will add support for allowing concurrent index space task launches to be colored so that point tasks can be grouped by colors. Point tasks that are all colored the same way will all be guaranteed to execute concurrently. There will be no guarantee of concurrency for point tasks assigned different colors. Legion will provide a default concurrent coloring functor (zero) that will map all the points to the color zero so that they are all concurrent.