Gnc-Prefs: rename preferences to be compliant with gsettings syntax rules

Syntax changes in short:
1. replace all _ with - in preference keys and groups (_ is not allowed)
2. base path should be /org/gnucash instead of /apps/gnucash

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23266 57a11ea4-9604-0410-9ed3-97b8803252fd