Porting #455 changes, and Fixes for issues #515,#516,#517

[aozien]

bldrs-ai#515:

• Have a single SelectionChanged message instead of selection/deselection
• The SelectionChanged message should be emitted regardless of the trigger

bldrs-ai#516:

• Add a new ModelLoaded message that is emitted when the model has been loaded
• From the automated tests, supply a local resource of an .ifc model instead of a network fetch to be independent of the network

bldrs-ai#517

• make selection of elements in tests more reliable through the side menu

To be done

The tests in load-sample-model.cy.js are yet to be fixed, since FindByRole isn't reliable in the case of the "Open Ifc" button, and that's what's causing the tests to fail.

check for possible searchIndex bug for IFCProject global Id