[Designer] Add the ability to detect when the active host container has changed as well as when the card itself has changed

[dclaux]

What platform is your feature request related to? (Delete other platforms).

• Designer

Is your feature request related to a problem? Please describe.
It is currently not possible for an application to grammatically detect when:

• The active (selected) host container has changed
• The card itself has changed
  Some partners need these capabilities in order to take appropriate action on their side.

Describe the solution you'd like
Two events are added to the designer:

• onActiveHostContainerChanged
• onCardPayloadChanged

Describe alternatives you've considered
No alternative.