Custom web item to trigger dialog should reuse existing dialog or remove the current dialog on close

This is only for the ESC key binding. The one in the footer works correctly and the one in the top right should probably be wired up manually (as its an additional one).

We should reuse the existing dialogs on the page when triggering a dialog. Currently we render another one and forget about the existing ones already on the page.

To reproduce:
Setup web item to trigger dialog
Click on web item to display dialog
Close dialog
Click on web item again and close dialog
Inspect DOM and multiple dialogs are present.

This causes problems when binding JavaScript event handlers to these dialogs when they are opened and closed.