Fix up emit_series

- [x] We need to have a concept in the database of which series are still configured, along with which tasks they are in
- [x] Deal with season jumping. SxEy+1 as well as Sx+1E1 could be problematic due to episode advancement. If it gets next season too early, it won't fill in the rest of the previous season.
- [x] An est_released plugin that estimates an episode's next release date based on the history of last found episode times.
- [x] Deal with possible different form of episode ids (S01E01 vs 1x01). Partially implemented, search plugins need updated to use `search_strings` field
- [x] sequence or date based show support? sequence should at least be doable, not sure how well it would come out.
- [x] When there is no history for a show in the database, we need to know where to start searching.
  - Discussed with paranoidi some, we are thinking eliminate 'watched' series option in favor of 'begin' or 'begin_from' option where you specify the first episode you want. This would be stored in the database. If there is no history in the database `emit_series` will start from there.
- [x] Also add a corresponding `--series-begin "some show" s02e01`
- [x] Injected-learn tv series, with produce an exception when series-begin is used on them and then query series status : http://pastie.org/private/eanpvjj3e6hz9cy3crkna (downloads or no downloads had been made for that series).
- [x] Loosen the backwards episode grabbing restriction to allow filling in any episodes in the past from the same season.
- [ ] We should implement some smart searching tvrage knowledge into emit_series somehow, and emit the proper entries and prevent emit_series rerun behavior in that case. (maybe this can wait for later)
- [x] Make api_tvrage persist info to the database
- [x] re-combine est_series and est_tvrage