make offline reading an option (collector bug)

[SJ]

Offline reading is a common request even for people who are regularly online -- you're going out to the park and want to take your books with you! let people use gnubook to read books online or offline, with minimal changes needed.

sub-bugs to be filed for this (are these bugs against gnubook, or against some other projet yet-to-be-named?):

1) add a "store this book offline" option at all times while reading
2) add a "personal bookshelf" view which shows books you have stored [online? or] offline
3) [gnubook-xo] add a "save as XO collection" feature for the XO that saves the book as an .xol library bundle

4) support reading lists / named collections of books.
4.1) add a "create a booklist" interface that allows for the definition of a list of books
4.2) from a bookshelf view, provide a "save shelf as booklist" option
4.3) [gnubook-xo] from a reading list or bookshelf view, provide a "save shelf/booklist as XO collection" feature that saves the set as an xol library bundle

5) define a Google Gears app that could support better offline browsing -- this could cache the index of available books and allow for offline booklist creation, for instance, so that you could queue up a few lists to download, and then download them all at once during a brief spurt of fast internet connectivity.

For more on xol bundles, see http://wiki.laptop.org/go/Collections