Add a per-login setting, on by default, that leaves books whose content files are all audio out
of the plugin catalog, its counts and bulk downloads, and drops a library holding nothing else.
The plugin detail page also names the first file the device can open as the main file.
Closes#1345
Squash of feat/koreader-widget-board. KOReader plugin 2.0.0 gets the widget-board dashboard, redesigned
book details, menus, lists and dialogs, Decor page and reading companions. Highlights, notes and bookmarks
now stay in step across web, Kobo, KOReader and the phones (defects D-00 to D-20, migration 0121), and
reading progress and narration hand off cleanly between devices.
neon