Add the credit test even if subtitles are not complete

I believe this matches the old behavior, but in any case it makes
sense.  The text is a request to subtitle the video on amara.
So even if there are not subtitles yet, having the link still makes
sense.  Now that I think about it "credit" is really the best word for
this.
For youtube videos sync to channels not owned by the amara owner (#1643)

This makes it so that if you link you're youtube account, then all
youtube videos for that account will be synced.  It doesn't matter if
you are the owner for the amara video or not.
Show the sync history tab for non-team videos

We still only show it for superusers though.
Honor send_subtitles_changed when saving SubtitleLanguages

Oops, not sure how I missed this one originally.
Don't re-sync imported subtitles (#1646)
Merge pull request #1648 from pculture/gh-1643

Gh 1643