Overhaul the layout/sizing settings

[tokenshift]

The different ways you can set sizing and layout options for the page gallery (orientation and columns vs. height and width, WTF does gutterSize even mean anymore...) are adding a lot of complexity, and aren't really useful when working with galleries across multiple devices. Consider simplifying this to have a "small, medium, large" + orientation approach, with default definitions of what those sizes are for different device sizes; then simplify/flatten the HTML and CSS structure so that it's easy to override via custom CSS snippets if desired.