create page via embed from file

[markmacgillivray]

demo-ed already but not currently active on the new site - should be possible to embed from an online file via viewer into any page - so the page is effectively created from the embedded doc / pdf / similar. Already code in place in web.py, but need to add back into the ui, and consider whether this means a page should have an editable content area too or not.

[markmacgillivray]

now ready to embed any url found in the record, so just need to add a way to add an embed url in the page settings

[markmacgillivray]

Done.