refactored OeREB interlis service to use timestamp from metadata table

This PR finishes the work on this ticket: https://github.com/geoadmin/mf-chsdi3/issues/461#issuecomment-39109823
by having the data status comment always visible and taking data information from the metadata table

@loicgasser you were right... it was really easy. What took me some time was nailing some stupid xml parsing errors ;)