Add detector specific commands

Add a way to implement detector specific commands (such as detector initialize or HV on/off).

The idea is to add a single det_command command to the Tango device (to keep generic) and then use some kind of json-rpc to serialize the commmands.

In the end, it is not too complicated and verbose to add specific commands and attributes:

// Factory method
static lima::tango::control_class<control_t>* create()
{
    return lima::tango::control_class<control_t>::init(
        "LimaSimulatorControl",      // name of the class
        {new initialize_command()},  // a vector of additional commands
        {new high_voltage_attr()}    // a vector of additional attributes
    );
}