Add integral refinement value to spatial coarseing interface

[jbschroder]

Assign an integral value in CoarsenRefStatus that indicates how “refined” or
“coarsened” you are from the original dt used when Braid was initialized. This will
eliminate any issues with numerical roundoff.

So, an integral value of "k" would indicate that "k*dt" is equal to the original dt
used when Braid was initialized.

This round-off can actually cause problems when trying to determine what "level" of refinement you're on.

This is not a high priority, though.