This way, when the user changes their color theme, any sheets
that did not have a specific color set will change with the theme.
Also add a button to clear color overrides from a sheet, because
any schematics that have been saved before this change will have
the colors set to something other than UNSPECIFIED.
When editing a sheet properties, the dialog always thinks the sheet filename is changed.
It creates serious issues, like duplicating all items in sheet, because the code try to
again import the existing sheet file content.
The temporary fix does not import the existing sheet file content if the
filename is not modified.
This is a very partial fix, because there are many other issues in this dialog
Jon Evans
jean-pierre charras
Jeff Young
Wayne Stambaugh
Dick Hollenbeck