Make older CC license versions available (not just 4.0)

[pb-amy]

Prerequisites

• Can you reproduce the behavior you wish to address with all plugins except Pressbooks deactivated?
• Are you running the latest version of Pressbooks, the latest version of McLuhan, and the latest version of WordPress?
• Are you experiencing the issue while using this book theme?
• Did you perform a cursory search to see if your bug or enhancement is already listed?

Description

Only the newest version of the CC license is available at this time (4.0). When a book admin makes their CC license selection from the drop down menu in Book Info on a book's admin panel, by default, that license is in version 4.0 (the newest version). We should make 1.0, 2.0, 2.5, 3.0 and 4.0 all available. License Versions on Creative Commons Wiki.

This is what it looks like on Book Info right now - it doesn't even contain the version number because it's presumed to be 4.0.

Expected behavior: In Book Info, the license options are, by default, the newest CC license version (4.0).

Actual behavior: We should have all the other versions available as well to choose from.

System Information

[SteelWagstaff]

TODO:

1. Allow version number selector at book level
2. Allow version number selector at chapter level
3. Change links for license display in webbook
4. Change links for license display in export files

Decisions:

1. only allow version #s to be set for CC licenses.
2. If empty, default to 4.0
3. Default value for new books should be 4.0, but can be changed by authors
4. Book clone operations should fetch/clone license type & number