Feature changes:
- Add book stats graph and refresh. By @webofpies in 154 and 162.
- 138: Separate Word Count and % Known into separate columns and support sorting.
- Allow term listing search in translations.
- 155: Add "words per page" field during book creation. By @fanyingfx.
Bug fixes:
- 112: show different options if backup failed (retry, skip, adjust settings)
- Sort statuses properly in the term listing.
- 95: editing pages updates book word count
- Shorten migration file names to prevent Windows file path length exceptions
Misc back-end:
- Add term Export CSV test.
- Calc book stats on at least 5 pages.
- Clean up some form styles.
- Speed up book stats calculation.