Refactor electric fields - remove unnecessary methods from modeler

Methods removed:
  .addElectricField()
  .removeElectricField()
  .setElectricFieldProperties()
  .removeElectricFieldProperties()
Update view to use new way of handling electric field events
Update Scripting API to use electric fields collection object directly
Update electric field tests

In fact they are almost unnecessary. We mostly test functionality
which is already tested in ObjectsCollection tests. However, as this
test already existed and fixing was quick, they can be useful as one
more integration test.