WDialog must always be resizeable

The API of WDialog was modelled loosely off of the ancient IE modalDialog and therefore allows size (width and/or height) to be set in pixels and resizeable is an option (albeit defaulting to true). A dialog of a fixed size which is not resizeable poses potential a11y issues for users who require a larger font, therefore dialogs should always be resizeable.

This would require an API change so has been scheduled for 2016 Q4. A client-side only fix could be implemented earlier with a configuration switch to allow a sub-theme to re-implement resizeability.

Should not have closed: the Java API still needs to be fixed by removing the resizeable member and its accessors.