Various server related things that I intend to get to soon-ish, in no
particular order.


New features for the in-browser viewer
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- When reaching the end of the book, show a popup that allows the user
  to rate the book and optionally delete it from the local storage.

- Allow loading fonts from the computer running calibre and using them
  for reading.


New features for the server generally
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- Add a way to search the set of locally available books stored in offline
  storage.

- Automatic Let's Encrypt integration so that using HTTPS is easier
  Should wait for the acme v2 protocol endpoint:
  https://letsencrypt.org/2017/06/14/acme-v2-api.html
  Turns out this fairly pointless to do, since it only works if the server
  is running on port 80, which is a privileged port.

- Some way to manage remote calibre server instances via the calibre GUI. Two
  possibilities are:
    1) Have the remote server appear as a "device" in the GUI. You can then
    send books to the remote server, update metadata, etc. just as you would
    when connecting calibre to a real device.
    2) Have the remote server appear as a library in the GUI
  (2) is preferable in terms of features/functionality, but is
  **much** harder to implement in a performant and semantically correct manner.
