Improve Code Climate Score

[haroldtreen]

Current Behavior

Some sections of the codebase have been slowly growing and becoming catch-alls for various bits of functionality. Code Climate is calling these sections out and the current score for the repo is a B.

Expected Behavior

• [ ] The Books class can be broken down. That class is currently handling database access, sanitization, validation and epub writing.
• [ ] The BooksServices class is pretty long.
• [ ] The ContentExtractor + HtmlProcessing classes are a bit long.

Issues to fix can be seen here: https://codeclimate.com/github/haroldtreen/epub-press/issues