ENH: Adding the base of a new tool fibertractdispersion

This new tool will be a conversion from matlab of the code

https://github.com/BRAINSia/CompressedSensingDWI/blob/master/MATLAB_SCRIPTS/compute_dispersion.m

to a c++ SlicerExecutionModel version.
BUG: the defaults for subsampling were zero, which made for endless loops.
COMP: add CompressedSensing
ENH: more checkpoint code
COMP: another partial work checkin
COMP: move functions/methods out of header files
COMP: Checkpoint -- adding more functions
COMP: partial completion checkin
COMP: finished coding phase
COMP: tweaking to fix some minor inconsistencies.
COMP: CheckPoint. Verified through calls to BuildSensor
COMP: fixed more issues.
COMP: more bugfixes
COMP: intermediate version of tvdenoise3. Doesn't converge
COMP: Fixed final problem keeping CompressedSensing from completing without crash
COMP: Cleanup
BUG: gradients returned from DoCSEstimate::computer were wrong
COMP: Fixed horrible memory leakage due to misunderstanding smart pointers
COMP: move BPDN_homotopy.cxx, re-write
COMP: bug fixes