rational approximation using direct solvers added

Added
- CStoreVectorAggregator base, CIndividualJobResultAggregator implementation, a unit-test
- CRationalApproximation base, CLogRationalApproximationIndividual implementation, a unit-test
- CRationalApproximationIndividualJob implementation, a unit-test
- CMatrixOperator base, a unit-test for shifting diagonals of dense matrix operators
- a new unit-test for CLogDetEstimator that uses rational approximation

Modified
- CDenseMatrixOperator