The OperatorInterface requires the ConstLincombOperator, the
LincombOperator and the MatrixBasedOperator and correspondingly binds all
these types now. They can be split over multiple compile units, since no
overloaded function in a single module is desired. From the matrix operator
we only want the factory method in a single module, so we split the type
bindings from the factory bindings.

This reverts commit e64f244a.