Adds excel import tool.

Current file imports 244 books.
Breaks down complex Book#read_excel method
Adds featured Books and Authors to homepage.
Adds livereload for easier frontend development
Merge branch 'coverflow'
Integrates featured books with coverflow
Puts badges on same line in README.md
Adds (very) basic books index and show, search and pagination
Adds coveralls
Encrypt .coveralls repo token and $SECRET decrypt config/settings.yml
Uses same SECRET for decription than the one stored encrypted in .travis.yml
Use a database.sample.yml, so I can keep using my local user instead of travis' postgres.