Method to add value domain to a representation

[florianika]

• Create a command AddRepresentationValueDomainCommand in Applciation/RepresentedVariables/Commands. Representation and ValueDomain should exist before executing this command. The command should contain this fields: long RepresentationId and long ValueDomainId
• The handler of the command should check existence of both representation and valueDomain and throw an exception if one of them is not found, else will assign the valueDomain to the representation.
• Add a new VariableRepresentation Closed controller and add the API PUT method that send the command to the handler.