Add libraries feature

Add the libraries feature, based on the versioning system.

Libraries are chosen for a book, and a library version is associated with a book version. A UI has to be created to configure the book.

A user interface displays a list of libraries which have been applied to the current book, with the following data for each;

• name
• a button to see which pages use the library

With a macro, the user can select which library content will be integrated in the book page content.