Change max levels after refinement (update Sync capability)

[rfalgout]

Update the Sync() feature to allow a user to do FMG refinement in the usual way, then once the desired space-time grid is constructed, change the number of levels in the solver. This is to help with debugging. It will require adding more Sync() access points in braid and also will require calling SetMaxLevels() (and possibly other functions) from within Sync() somehow.

See closed pull request #23 for more details.