Update backend to use conversion service

[tarelli]

• [x] Create ServiceRegistry to manage what input/output format is connected to the different Services
• [x] Enable backend code to use the conversion simulator if specified by the user (see schema extension) or if needed (the format returned by the ModelInterpreter doesn't match with the format accepted by the specified simulator, look for registered conversion service that can take care of this conversion or return an error if none are present)
• [x] Add API method to the backend to getSupportedOutputs
• [x] Add API mothed to the backend for writeModel