Add plot marker visible property

[mnabywan]

We included the marker visible property.
I have updated the example in app/display/model/src/main/resources/examples/plots_xy.bob - I added a rule to make the marker visible.

Checklist

• Testing:

  • The feature has automated tests
  • Tests were run
  • To test check example in app/display/model/src/main/resources/examples/plots_xy.bob

• Documentation:

  • The feature is documented
  • The documentation is up to date
  • Release notes:
    • Added an entry if the change is breaking or significant
    • Added an entry when adding a new feature