catchall embedding for og:video metadata

2. video/audio elements were not replaced with text links properly in
low bandwidth mode

update_daemon_common: do not abort entire batch if PDOException happens when processing individual feeds

API: getHeadlines: return feed_id for Archived entries as 0 instead of null to be consistent with requested feed_id

parser: move media:element handling to feeditem_common; use media:content @media attribute to generate placeholder content-type if not specified

Revert "add (hidden) _NGINX_XACCEL_PREFIX which uses nginx X-Accel-Redirect to serve static files faster"

This reverts commit c5c3a0a2.

split transparent rewriting of locally cached media URLs to execute after both sanitize() and HOOK_RENDER_ARTICLE to allow plugins work on original source URLs consistently

Some RSS feeds contain multiple enclosures with the same URL. When the first of
these is not recognized as an image, later entries are not added to the
database as rows in ttrss_enclosures. This change differentiates enclosures
based on their content type, so an entry can have multiple enclosure types with
the same URL (but possibly a different content type).