simplified content setting

I noticed that content was not getting cleaned properly on wikirate.org and started poking around
all these things need to get run on update, not just create. (cleaning, clearing drafts, etc).

I think what may have been confusing is that in the old version (eg https://github.com/wagn/wagn/blob/7442c319ece73630b570a5cfdb8045ed37c29b52/mod/core/set/all/tracked_attributes.rb) only appears to have one call of #set_content, but it's also called from line #4 in #set_tracked_attributes.

The special from_trash handling was because there had to be special handling of revisions of cards that had been in the trash before, since those were the only new cards that had an id before the revision was created.  Since we now always create the card first, this is no longer an issue.