Allow images grid mode to be set from API

[Toutouwai]

Short description of the enhancement

It would be useful to be able to force a particular grid mode (square, proportional, list) for an Images field via the API. Currently you can set the gridMode property but the actual layout of the inputfield can be overridden by the cookie in the visitor's browser, so often setting the gridMode has no effect.

Maybe this could be solved by adding a useCookie option which would determine whether the cookie affects the inputfield layout or not.