Create an IsContentModified() function in each frame
that provides if the content has been modified, and
use that instead of always copying the checks.
* Make the grid display settings separate from the board object
* Ensure that the grid is initialized on creation in all the frames
Fixes: lp:1843169
* https://bugs.launchpad.net/kicad/+bug/1843169
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.
3 layers shown (but not selectable) in layer manager are removed from layer box
(inner_layers is a pseudo layer, Edge_Cuts and Margin are not yet managed in Fp)