Ambiguous analyzer for OffspecSimulation

OffspecSimulation contains and uses members OffspecDetector and IBeamScan and each of them has its own analyzer.

Now IBeamScan::analyzerMatrix() is used for computation in OffspecSimulation::runComputation.

For reasons of consistency, we should use OffspecDetector::analyzer().matrix() instead.

Moreover, IBeamScan::analyzerMatrix() should be hidden (only for offspec) from users to prevent ambiguity.