Remove obsolete enable_euro key from gconf

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23211 57a11ea4-9604-0410-9ed3-97b8803252fd
Cleanup after file backend settings refactoring

This affects many other components as well, including the
python bindings

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23212 57a11ea4-9604-0410-9ed3-97b8803252fd
Whitespace cleanup, comment improvements and spelling fixes

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23213 57a11ea4-9604-0410-9ed3-97b8803252fd