CORAL-131: pass information about requested resource classes to
ResourceHandler.getData(..)
CORAL-131: load data for all persistent (tabular) constituent classess
of a resource class using a single JOINed statement
CORAL-131: dropped unused RetrieveView
CORAL-131: implemented partitionByHandler correctly - all handlers of
the same class are equivalent, irregardless of particular ResourceClass
they are bound to.