fix duality gap calculation
rename p and k into iteration
add tests for frank wolfe pickling and batch version.
fix:  make test easier so that we can use qpbo
use "dual_objective_curve" and "primal_objective_curve" everywhere instead of "objective_curve"

Conflicts:
	pystruct/learners/frankwolfe_ssvm.py
refactor loggers big time :)
use either primal_objective or dual_objective everywhere.
FIX some calls to loggers