Allow pop-up to be default or have a button on the main window to turn it on

**Describe the feature you want:**
I would like a way to either make the Pop-up mode the default, so that when you click on the extension, the window with the code opens in the pop-up window mode every time
Alternatively, a button on the title bar (when the Settings, Lock, Scan and Edit buttons are), to switch to pop-up mode with one click.

**Why do you want this feature in Authenticator?**
I use Google authentication to secure sshd on servers. If I open the Authenticator extension to get a code and then click into my terminal windows, the extension closes immediately & I can't see the code to type it into my terminal, which is really frustrating.
If there was a way to keep the code on screen when you switch focus to another program, it would make this extension far more usable. I assume you can't keep the normal extension window from closing as soon as Chrome loses focus and that's why you created the pop-up mode, However it's too clunky to have to click on Settings, Preferences, Popup mode to enable it each time you want a code.
Otherwise this is great extension - thanks for creating it :-)

Inizia tracciando il comportamento del clic sull’estensione e il flusso Settings > Preferences > Popup mode. Decidi come si inserisce nell’UI esistente l’azione predefinita richiesta o l’azione con un clic sulla barra del titolo; il lavoro è completato quando il codice rimane visibile dopo il passaggio a un terminale o a un altro programma senza dover abilitare ripetutamente la modalità popup.

Scritto dal modello di indicizzazione a partire dal testo della issue.