Gnc-Prefs: migrate most preferences found in app-utils

This required  changes in dependent modules as well. And obviously
the gnc-gconf-utils.[ch] files are not removed yet. Too many
other files still require those.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23228 57a11ea4-9604-0410-9ed3-97b8803252fd