Fixed regression introduced in 3.10.0, with stale facade properties sticking
around in the case of "no subscribers".

Added unit tests for both the subscriber and no subscriber case.

All unit tests pass:
✔ [Total]: Passed: 10859 Failed: 0 Total: 10954 (ignored 95)

Slider functional tests pass.
Slider examples work manually.

This impacted slider's thumbMove defaultFn which was using a "source" property
added to the facade to figure out whether to set the value or not, and
commonly had no listeners (only surfaced by manual testing, which was why
it got missed - unit and functional tests all passed).
Added on subscribers fresh facade test also
Added on subscribers fresh facade test for real this time
Merge branch 'slider-regression-event-fix' into dev-master
Build for event fix for slider regression. Cleaning up stale facade props

All tests pass:
✔ [Total]: Passed: 10860 Failed: 0 Total: 10955 (ignored 95)