fix constness of setOperationCallerImpl functions

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
internal: fix for explicit instantiantion of Operations and friends

Signed-off-by: Ruben Smits <ruben.smits@intermodalics.eu>
Merge pull request #37 from smits/explicit_instantiation

Explicit instantiation