Add SumFunctionalConstrainedLinearization class

Just as SumFunctional implements the sum of several independent
functionals, this new class SumFunctionalConstrainedLinearization
implements the sum of linearizations (or, equivalently, the
linearization of the sum).
2 jobs for add-sumfunctionalconstrainedlinearization in 5 minutes and 8 seconds (queued for 2 seconds)