More fixes for Ourmedia

I've been fixing a number of bugs. The main one related to how media pages were displaying media. There were a lot of problems with MP4 and other files due to some old embed code and a missing file. Things look and work much better now.

I also fixed a pet peeve. Long lists for "My other media" are now truncated to the most recent 12 posts and have a link to a separate page listing all media for that user. This makes for much cleaner media pages (and faster loading too).

While testing, I discovered that sometimes there is a media post on Ourmedia, but the item has been deleted at Archive.org. This makes Firefox display a message about a missing plugin due to the fact that it is serving up a "media removed" page instead of the media. We need to detect and handle this better.