EPlugin: update the ACL add sub-dialog before displaying
EPlugin: update the ACL add sub-dialog before displaying

* update the "add" variant of the ACL add/edit dialog with
  data previously read from the server
* we fill the combo box with the access_id entries we have
  for the folder, but do not set a default
* the combo box entry field is thus empty to clarify that
  we're adding a new entry, but the already-existing
  access_ids appear when the dropbox is opened so we can
  pick one and change it (should ease editing in some
  cases)
* once we can query address books or directory services
  via the "Retrieve" button, more access_ids could be
  added to the combo box for easy selection

GNOME/evolution-kolab,GNOME/evolution-kolab