Second NLIN check-in. Class still being tested.
Main changes:
1. Addition of minctracc module with defaults that match current MBM defaults.
2. Masks are now properly set when each nlinFH is instantiated.
3. Multiple changes to mincatoms, including:
3a. mincANTS now correctly uses target_mask instead of source_mask
3b. default minctracc similarity parameter is now 0.8 (matches command line default)
3c. -use_simplex, -debug and -max_def_magnitude added to default nlin minctracc command.
3d. -identity is now default for nlin registration if there is no previous transform (previously this was only true for lsq12)
3e. Fixed errors with mincAverage
4. Cleaned up a couple of redundant lines in RegistrationFHBase

This check-in also includes some temporary changes, which will be removed after testing is complete:
1. Hardcoded ANTS blur of 0.056
2. Harded coded blurs and steps for minctracc
3. -sinc is used for resample--we may or may not want to keep this.
4. -tol and -xcorr added to nlin minctracc atom, even though they only make sense for linear reg. I did this to be consistent with current build model for testing. Will remove when complete.