Remove calls to feed.js
Added schema upgrade to delete the tid:lastFeedUpdate key
Removed storage of tid:lastFeedUpdate now that feeds are on-demand
Changed feeds to be generated on-demand

No longer are we writing them to disk, instead, we simply generate on demand.
Change Feed.forTopic to cap at 25 items, not infinite
Merge pull request #979 from miksago/ondemand-feeds

On-demand feeds