Feature/algebra

Okay, main changes:

Tests for CSCMatrix Operators under OptimizationSpace
FrobeniusMatrixNorm is better
Minor refactor to CSCMatrixOps 

There was a case where I didn't notice that an implementation was missing because a default implicit for the operation was found in Vector which used activeIterator (and was therefore very slow..). Note was a reminder to check that all the generic implementations are specified. I think this is now the case, but I'll check again before the next PR.