Update objective in the algorithm base class - can we write it as a default callback?

[MargaretDuff]

Description

Can we move this to a callback?

CIL/Wrappers/Python/cil/optimisation/algorithms/Algorithm.py

Lines 188 to 190 in b91c0eb

	def update_objective(self):
	'''calculates the objective with the current solution'''
	raise NotImplementedError

Environment

import cil, sys
print(cil.version.version, cil.version.commit_hash, sys.version, sys.platform)