implement create_or_get_series controller

Ripped out this piece of logic to make SeriesHandler simpler.
implement create_or_get_chapter controller
chapter.series_name; better series update; tolerant bookmarks; thumb_url

- Chapter now has series_name
- Implement update_series() controller that can update all of its
  chapters with the latest series name if it has changed
- Bookmark APIs now reuse create_or_get_series/chapter(), so even if I
  delete all series/chapter records, the series/chapter bookmark APIs
  won't break.
- series_info() now returns thumb_url instead of thumbnailUrl for
  consistency.
better My Chapters route
show series name in chapter page title
add JSX comment to chapter_bookmarks
fix typo last_updated >> last_update
don't try to update series in SeriesBookmark API

Add "no_update" param to create_or_get_series(). This is useful for
SeriesBookmark, since the first request needs to finish quickly in order
for the client to at least display series thumbnails and start fetching
new chapter data.
ignore chapter name from chapter url when fetching

Chapter name in URL may include illegal chars that will make pytaku's
GET request fail. Replaced it with "_" to be safe.