Add login modal options to hide details, callback

When invoking the logInModal, you can now request that the anonymous option
and the extra info be hidden, for when you require a login for a specific
change. Use case in mind: Forking while not logged in.

The logInModal method now returns a promise that is resolved upon login,
or rejected otherwise, so that you can hang a follow-up onto a login.
Prompt for login when forking as anonymous.
Merge remote-tracking branch 'origin/master' into fork-improvements-episode1
required config for metadata stuff in bookish
static metadata for source of books
add metadata logic to opf file model
Use correct terminology: copying the book shelf.
Fork improvements.

* Allow forking into an organisation
* look for an existing fork
* Poll until fork is complete
* update url to indicate book switch
Add progress indication modal.
Merge remote-tracking branch 'origin/master' into book-metadata
Check for duplicate repo also in organisation

The previous version only checked for duplicates in the user area.
If there is an existing fork, offer to take me there.
Merge remote-tracking branch 'origin/master' into fork-improvements-episode1
Instead of fetching list of repos, call getInfo to see if it is there.
write metadata into nav file header
updating metadata stored in nav file
getInfo takes no parameter. Cleaning up.
Merge branch 'master' into book-metadata
fix book metadata to use prefixed attributes
Merge remote-tracking branch 'origin/master' into fork-improvements-episode1

Conflicts:
	scripts/gh-book/auth.coffee