Detach "Generate Address" box from main window

[Anderson Nascimento Nunes]

As it is now, the user must close the "Generate Address" box to use the main Thunderbird window.

It would be handy to have the add-on box detached from the main window, so both could be open at the same time without interfering with the other.

That way the user could more easily generate multiple addresses, as there would not be the need to close and open the add-on box every time (if he/she also needed to use the main window between each address generation).

This is a "would be nice" type of enhancement. Other changes take priority.