Tweak footprints().
New aging logic to keep all of yesterday's episodes.

Change the DB format to allow more than one old-episode at the start of
the episode list (plus a few other more minor DB changes).  Tweaked the
way we grab the episodes from TheTVDB API so that the loss of all the
formerly-known recent episodes doesn't leave us with no prior-episode
info (the code used to have to make another request of older episodes).