This code is ugly and terrible but it works™. Previsously when a download
would finish it would refresh all the views. Now the if the widget get's
into the Donwloading state, it will setup a callback that will check
periodicly if it's still downloading and update the widget state when
the episode stops downloading.
While ideally we want episode widget to determine their states
themselves and avoid refreshing the whole view, currently there
is no infrastructure for that which resulted in views not being
updated their EpisodeWidgets stuck in the InProggress state.
Previously we would refresh all the views when download/cancel
button was clicked. This was done mainly to avoid zombie widget bugs
that would arise from shared state.
Now we still refresh all the background views but not the visible one.
Instead the widget has the reponsibility of recalculating it's state.
request_constructor is now a Source method.
update_etags now takes &mut self instead of mut self.
update_etags now uses source setters methods instead of raw fields.
changed the naming of into_feed to to_feed according to rust convention.
Tried to have a seperate futures loop but it's too confusign having
too write a Trait2, functon2, etc version of everything and keep it together.
Futures are functional sort of, so the synchronous versioun can be removed.
It still needs a ton of work though to be ready, or even get near the perf
of of the sync+rayon version.
