Updated Readium.js to the version with zipped EPUB support.

Added a small zipped EPUB example.

Removed leftover redundant stuff.

Reverted to vanilla bootstrap.css and Remove unused bootstrap.min.css.

Extracted Bootstrap CSS customizations to a separate CSS file.

Introduced Grunt build with tasks for:

* running an embedded Express web server,
* updating Readium JS libraries by downloading latest versions from GitHub.

Updated the README file.