avoid potential performance issues when the dialog is still listening to
the board updates and refreshing its data and view structures.
it seems useful to keep the settings of the dialog across dialog
open-close cycles.
The pointer passing for display options is deprecated. This removes the
excess casting as the EDA_FRAME didn't need the base call with no value.
All requests for display options are now returned const and are updated
with a Set() routine after modification.
In Gerbview, this resolves an issue where the display options were not
stored because it was receiving the NULL from EDA_FRAME.