Fix an issue where server select menu was not working in settings page

[yuya-oc]

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Summary
Fix an issue where server select menu was not working in settings page.

In v3.5.0, the behavior of #443 is expected because the config is not saved yet in the settings page.
Now the config is auto-saved, so I added an event listener for menu items.

Issue link
#443

Test Cases

1. Open the settings page.
2. Select a server from the tray icon menu or "Window" menu items.
3. The selected server' tab should be shown in the main window.

Additional Notes
https://circleci.com/gh/yuya-oc/desktop/167#artifacts

[jasonblais]

+1, works for me. Great work @yuya-oc!

[jasonblais]

@yuya-oc might be okay if you helped test this on Mac, so we can get it in to 3.6

[yuya-oc]

I see. Tested on macOS 10.12.2.