Prevent heartbeat from rescaling OPI graphs when I have defined custom scaling

As a user, when I define a custom scaling on an XYGraph widget in an OPI, I don't want the heartbeat to reset the scaling because it makes it very difficult to view the data I want.

Notably, custom scaling of XYGraphs is only accessible as an advanced option through the CSS contexts menus. Two possible solutions are:

1. Switch off the heartbeat when a user defines a custom scale
1. Don't allow users to define custom scales