Web eID dialog disposing

TODO: Add a diagram that depicts the call and event chains that cause the Web eID dialog to be disposed and deleted.

Dialog disposal is quite complex as there are a number of different scenarios that cause the disposal:

1. retriable error occurs, user clicks Retry,
2. fatal error occurs,
3. user clicks Cancel on the dialog (window destroyed signal is connected to controller exit signal),
4. user clicks OK on the dialog (window destroyed signal is connected to controller exit signal),
5. user clicks Cancel on the PIN pad (window destroyed signal is connected to controller exit signal),
6. user clicks OK on the PIN pad (window destroyed signal is connected to controller exit signal).

Connecting window destroyed signal to controller exit signal assures that the window has been properly disposed when the controller exits.