Numerous changes to simplify and streamline stats calculations. Related to Issue #91.

Biggest changes:
1. Scaled jacobians now calculated with full non-linear transforms, using either inverted lastXfm from input to target, or concatenating an additional specified xfm.
2. Jacobians calculated with pure non-linear target to input, concatenated with linear part of input to target. Concatenation now done correctly.
3. Removed the ability to subtract out an average displacement (see Issue #91). We may add this back in the future, but for now, it is gone.

Specific implementation details:
1. Lots of general clean up of CalcStats and CalcChainStats. To wit:
1a. linAndNlinDisplacement now a single function for both CalcStats and its child class, CalcChainStats. Differences between the two are encapsulated in the calcFullDisplacement and calcNlinDisplacement functions. calcNlinDisplacement itself a new function!
1b. Removal of average displacement calculation (e.g. in __init__ and setupDispArray calls, as well as removed code in linAndNlinDisplacement)
1c. calcDetAndLogDet now called twice in fullStatsCalc: once with pure non-linear displacement (jacobians) and once with full displacement (scaled jacobians)
1d. createOutputFileName function condenses three functions into one!
1e. Clean-up of calcDetAndLogDet to address 1c. and just generally be more streamlined.

Other minor changes:
1. Fixed small bug in setting the NLIN minctracc registration protocol. (Name is reg_protocol, not nlin_protocol.)
2. In NLIN modules, setLastBasevol now called in final iteration after registration complete, so that lastBaseVol in new "final" group is set properly.