Allow incrementing seen episodes in the series list view

[JoosepAlviste]

Showing the last seen episode and allowing the user to click on the plus button to mark the next episode as seen.

Blocked by #39 and #37

TODOs:

• Update series progress when an episode is marked as seen or not seen
• Update series progress when new episodes are added (through sync)
• Handle case when some episodes are not seen before the episode that's marked as seen or not seen
• Handle case when there are more seen episodes AFTER the episode marked as seen. E.g., seen are s1e1, s1e3, and the user marks s1e2 as seen, the progress should have the latest episode as s1e3, not s1e2
• Marking season as seen should update latest and next episodes info in list view (in the cache)