Check if we should redirect to some other content in a model.

This allows a container object to redirect editing to some representative
object in the container. For example, the first module in a book.
Opening a book redirects to editing the first module in the book.
Merge remote-tracking branch 'origin/master' into open-first-module-with-book
When switching repos, open the first book on reload.
Merge remote-tracking branch 'origin/master' into open-first-module-with-book
Allow contextModel to be null.
Revert "Check if we should redirect to some other content in a model."

This reverts commit 993bf1876a497a22487131f14f4b852baaddfba2.
Revert "Opening a book redirects to editing the first module in the book."

This reverts commit 5ea40c05060800fcb1794dcc81b04f7b001d21ce.
Explicitly find first module and edit book in context of opf.
Merge pull request #78 from oerpub/open-first-module-with-book

Open first module with book