implement "auth if possible"
implement read_list

- User model now has read_list, which is a list of Title keys
- Implement User.add_to_read_list()
- Implement Title.is_in_read_list()
- Title API returns `is_in_read_list` that tells if the Title is in the
  logged in user's read_list
getByUrl => get_by_url
implement read-list API

- Implement ReadListHandler + 'read-list' API endpoint
- Add "site" field to Title model
implement "add title to read_list" API

Also fixed PyError() invocation in ChapterHandler to use a dict as
param, not a plain string
add readlist route
Implement "add to read list" button

- Refactor all title state to <TitleInfo>
implement PytakuApp.ajax that only provides auth header when logged in
run_list => read_list
encodeURICompnent for everything that's used in GET. Plain URL for the rest.
avoid repopulating title info
display latest chapters in read list
implement removing title from read list
add chapter_limit for title API
title name in readlist links to title info page