Rename "Collection" to "Book" and "Module" to "Page"

This changes the name of the search filter.

Also changed mediaType to "application/vnd.org.cnx.collection" and
"application/vnd.org.cnx.module"

Close #230
Merge pull request #231 from Connexions/rename-module-and-collection

Rename "Collection" to "Book" and "Module" to "Page"