Fix picture views recomputation APIs generating a 'document modified' audit trail entry

It is possible to recompute the picture views of a document storing an image through different APIs:

• the JSF UI administration page http://localhost:8080/nuxeo/nxadmin/default/default-domain@view_admin?tabIds=MAIN_TABS%3Aadmin%2CTREE_EXPLORER%3Anavtree_CONTENT_TREE%2CNUXEO_ADMIN%3AImaging
• the automation operation Picture.RecomputeViews
• the bulk action recomputeViews

The problem is that using the JSF UI administration page or the automation operation Picture.RecomputeViews, it generates a documentModified entry in the document's audit trail, while the bulk action recomputeViews. Also dublincore properties of the document should not be updated (dc:modified and dc:lastModified).