[Feature request] Have a "Help > About" menu and dialogue

I know that a trip to the cli and `keybase status` can tell me information like this, but having an About dialogue with version information would be very helpful and in keeping with a traditional GUI.

Start by reviewing the information exposed by `keybase status` and how the existing GUI organizes its menus and dialogs. Define the platforms and version details the new Help > About dialog should cover, then verify that the dialog presents that information consistently.

Written by the indexing model from the issue text.