Refactoring of the LineSearchMinimizer.

1. New LineSearchDirection interface, factory and instances.
2. Cleanup of LineSearchMinimizer to use the State and Direction objects.
3. LBFGS -> LowRankInverseHessian.
4. Refactoring of the RunCallbacks function and share it across
   LineSearchMinimizer and TrustRegionMinimizer.

Change-Id: I19354afc6f5d6567b28918710c2012dc30ef8f32
12 files changed