ENH: Improve logic for choosing registration mode.
ENH: Improve T1 only segmentations

For T1 only images, sometimes the
globus does not have enough contrast
and it is overwhelmed by other structures
and ends up being squeezed out.  This
results in too few samples for the KNN
estimates.

In this version, if a label as too few
samples, then that prior is given increased
priority until sufficient samples are available.
ENH: Optimize registration parameters for ANTs template building.
BUG: Command line to limit subjects to process was incorrect.
STYLE: Hide debugging information.
ENH: Fine tuning ANTs registration to take less time

ANTs registration was taking far too long to run.  Make parameters
closer to antsRegistration so that run times are more reasonable.
ENH: By pass denoising for BCD failures
ENH: Limit the number of iterations for full size SyN

When doing full size SyN, the tolerance needs to be much less
in order to ensure convergence in a reasonable amount of time.