Change the "Window" menu title? #53

When there are multiple tabs, the window menu would look like:

<img width="344" alt="Screenshot 2020-06-08 at 22 19 57" src="https://user-images.githubusercontent.com/170270/84041272-31b0fe80-a9d6-11ea-9616-ab82237207bf.png">

Where General is the preferences window title. However, I feel it's not clear enough to the user that General mean the preferences window. Also, what if the main window has a name that is the same or close to the preferences tab name. That would be confusing.

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When there's no tabs, the HIG says that the window title should be the app name and then Preferences, but that can look weird:

<img width="344" alt="Screenshot 2020-06-08 at 22 18 38" src="https://user-images.githubusercontent.com/170270/84041163-134b0300-a9d6-11ea-8099-ba78c34df379.png">

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The macOS Human Interface Guidelines doesn't say anything about this.

My preference would be to use Preferences — General for the title in the Window menu when there are multiple tabs, and Preferences when there's none.

Xcode uses this convention: <img width="362" alt="Screenshot 2020-06-08 at 22 22 42" src="https://user-images.githubusercontent.com/170270/84041586-98361c80-a9d6-11ea-9043-456288d529e5.png">

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Changing the title of only the "Window" menu items is possible with:

NSApp.changeWindowsItem(window, title: "Preferences — General", filename: false)

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Thoughts?