Add WAM-specific title generator plugin.

This was originally going to be in a separate repo but there has
been a change of tack.
Merge pull request #6 from leftclickben/AddWamTitleGenerator

Add WAM-specific title generator plugin.
Add WAMMultipartIDNumber.php
Merge pull request #7 from leftclickben/AddWAMMultipartIdNumbering

Add WAMMultipartIDNumber.php
Merge branch 'master' of https://github.com/wamuseum/providence into InitialMergeInvestigation