Drop check for glib >= 2.14, glib >= 2.28 is already required

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23311 57a11ea4-9604-0410-9ed3-97b8803252fd
Add default-to-save timeout on save-on-changes dialog

If the timeout is reached, the dialog is closed as if the user clicked on save.
The timeout period can be set via the preferences dialog

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23312 57a11ea4-9604-0410-9ed3-97b8803252fd