Revert "store originally uploaded XML instead of marshalling to ISO for uploaded metadata"

This reverts commit 27cac2a7d0a52a9abf55ac63a5070b5a611684a0.
Merge branch 'master' of github.com:GeoNode/geonode
Merge branch 'master' of github.com:GeoNode/geonode
default is always ISO
move download_links to ResourceBase, extend LINK_TYPES
Merge branch 'master' of github.com:GeoNode/geonode
Merge branch 'master' of github.com:GeoNode/geonode