Set a minimum height (for small displays)
Set a minimum height (for small displays)

Without a minimum height on mainTabWidget, Qt uses the sizeHint as the minimum
sizes, and we end up with a main display that can't be shorter than 603 pixels.

For reference, the default Ubuntu 14.04 GUI (on a 640x480 screen) allows up to
456 pixels high for a maximized window, or 428 for a non-maximized one.

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