EBookBackendSqliteDB: Added e_book_backend_sqlitedb_get/set_locale()

Locale setting is now only ever guessed when creating a new addressbook
before e_book_backend_sqlitedb_set_locale() is called, setting the locale
will save the localization setting and it will be reused on subsequent
accesses. If and when a locale setting is changed, the contact sort
keys are regenerated with a new ECollator for the new locale.