Add a generic property getter that does not require specifying the type

[fingolfin]

In NormalizInterface we allow this.

Relevant function there is _NmzConePropertyImpl, some code snippets from that:

template <typename Integer>
static Obj _NmzConePropertyImpl(Obj cone, libnormaliz::ConeProperty::Enum p)
{
    Cone<Integer> * C = GET_CONE<Integer>(cone);
    ConeProperties  notComputed;

    SIGNAL_HANDLER_BEGIN
    notComputed = C->compute(ConeProperties(p));
    SIGNAL_HANDLER_END

...
    switch (libnormaliz::output_type(p)) {
    case libnormaliz::OutputType::Matrix:
        return NmzToGAP(C-> getMatrixConePropertyMatrix(p));

    case libnormaliz::OutputType::Vector:
        return NmzToGAP(C->getVectorConeProperty(p));

    case libnormaliz::OutputType::Integer:
        return NmzToGAP(C->getIntegerConeProperty(p));

    case libnormaliz::OutputType::GMPInteger:
        return NmzToGAP(C->getGMPIntegerConeProperty(p));

    case libnormaliz::OutputType::Rational:
        return NmzToGAP(C->getRationalConeProperty(p));

...


    case libnormaliz::OutputType::Complex:
        // more complex data structures are handled below
        break;

    case libnormaliz::OutputType::Void:
        // throw "cone property is input-only";
        return Fail;

    default:
        throw "unsupported output_type";
    }