Allows reports to derive from other reports and then change the option
default values to suit. If they change only the values and not the defaults
then it's possible to create saved report configs that don't include the
options whose values are changed to the base report's default value. See
https://bugs.gnucash.org/show_bug.cgi?id=642292.
To support a variation available in dialog-options. Even though it's not
used in any GnuCash code nor documented anywhere it might be in some
custom reports.
From std::string. The consumer is a GtkWidget so we might as well do the conversion
inside the class and this will simplify adding these functions to GncOptionDateValue
in the next commit.
So only GncOption and the GncOptionDB free-function interface are public.
We don't want to expose template headers widely, it would blow up compilation
times and might lead to one definition rule violations.
