Add Feature to allow runtime changes to joint limits

[peci1]

I'd like to change <limit><velocity> and <limit><effort> dynamically during the simulation. Currently, it seems that these values are only read when parsing the model.

I've tried this, but changing the component data has no effect:

auto axisComponent = _ecm.Component<components::JointAxis>(this->joint);
axisComponent->Data().SetEffort(2.0);

I also tried re-creating the component, but that also doesn't change the physics engine behavior:

auto axisComponent = _ecm.Component<components::JointAxis>(this->joint);
axisComponent->Data().SetEffort(torque);
components::JointAxis axis(axisComponent->Data());
*axisComponent = axis;

[scpeters]

Your code snippets are from ign-gazebo, but this is an issue with ign-physics because there is no Feature that exposes joint limits via the API.

[scpeters]

I think a Feature API could be added to Joint.hh

[scpeters]

feature was added in #260