Follow File Name Conventions

File naming conventions now state that all PHP files (except templates) should
be lower-case and use underscores to separate words in a filename.

There is another pull request in place that modifies IslandoraBookReader.js
It may be best to wait till its pulled and then merge with this before pulling.
Merge pull request #8 from nigelgbanks/7.x-filename-conventions

Follow File Name Conventions