Added user preference to change layout width

Created by: gopeter

As discussed here, I've added an option to choose between a small and a wide application layout. Since there aren't tests for such UI helper classes/functions (like the fluid_layout function), I don't added tests for this feature.

To achieve this, I've added a new column to the user table which stores the layout option and extended the fluid_layout function which now uses the user preference.

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