Creator : Execute property widgets inside the activity

In the Creator, inside the property editor for actions, users can specify values for each property of the action. In the case of a UAM property, the widget selector is executed, which displays a mask on the screen and unmasks the widget under the mouse, which allows for simple selection.

Since we moved the Creator to the service, we cannot rely anymore on the old property editors as they assumed that they would be ran inside the current activity. Right now, all the property widgets are executed inside the service. This causes problems only for actions, as they have no way of executing a particular selection widget inside the current activity.

The solution to this bug will allow the execution of custom selection events inside the current activity. This will notably be applied to the Change Color addon, which needs to select a widget inside the activity. A mechanism must be devised to allow communication between the Probe and the Creator to be able to run those selection widgets.

One way this could be done is by re-using the existing createEvent method on the Probe and sending custom Creator-only events, with a single mandatory property being the one that is desired for the action in the Creator. Since we enforce the execution of all the property widgets for all the mandatory properties of an event already, this would provide with a quick and easy way to pull off this communication without modifying the interfaces for both the Probe and the Creator.