ENH: Add currentIteration to LBFGSBOptimizerv4

A helper class (LBFGSBOptimizerHelperv4) is wrapped around vnl_lbfgsb.
This class is used to translate iteration events from vnl_lbfgsb
into iteration events in ITK.

We also needed a wrapper helper for the base class since part of
optimization is done by the base class.

Change-Id: I9372a9f16766a0214d15857e295a59cf513b6b64
Merge topic 'currIterForLBFGSB_r'

1ddfea41 ENH: Add currentIteration to LBFGSBOptimizerv4