[FEATURE] Time-based statistics meta for books

[aaronleopold]

Is your feature request related to a problem? Please describe.

I'd like to be able to configure the following:

• Average page-read time for image-based books
• Average WPM for other books (i.e. ebooks)

In order to compute an estimated time to read / time left until finished statistic.

Describe the solution you'd like

• Introduce a new analysis task for counting the words in an EPUB file
• Implement basic function for estimating remaining word count based on current place in epub
  • This can be a rough estimate based on the percentage, or more accurate if counting from the current epubcfi string
• Implement basic time estimate functions for:
  • Time to read X words based on Y/min configured rate
  • Time to read X image-based pages based on Y/min configured rate

I'd love to then someday support showing people things like:

• You've read X words
  • Estimated WPM based on start/end times of finished books and corresponding word counts
• You've read X pages