Add option to allow only one instance of the application

I’m using the new option of the desktop app to always show a tray icon, but I have a problem using it: when I «hide» the application (using the Shift+Ctrl+M shortcut) and try to restore it by clicking on the launcher, another instance of Bitwarden is spawned and shown, instead of the already running one.

I guess the solution would be to add an option to allow only one instance of the application to run.

I’m using the snap version of the application with Ubuntu 16.04 and Unity 7.

Well, it seems that this is already the case:

But that it only works when the window is not «hidden» to the system tray…anyone knows why?

Opened https://github.com/bitwarden/desktop/issues/324 as I now think that this is a bug.