Update and clean up settings

This patch updates the format beta1 settings and up to current settings. It also cleans up some variable names: feedapi_update_existing and feedapi_items_delete should be called update_existing and items_delete - like refresh_on_create. It also drops the columns items_delete and update_existing - which are not necessary any more.

This patch needs testing on a
* pgsql system
* update from a running feedapi drupal-5 dev version system with mixed beta1 style and dev version style settings storage*)

-
*)
beta1 style settings storage: items_delete and update_existing are fields in db
dev version (up to revision 1.23.2.95): items_delete and update_existing serialized in settings field (settings[items_delete], settings[update_existing])