Set up Karma for JavaScript unit tests

This is a rather large commit that:
 * Configures Karma
 * Provides a bundle command, to bundle our JavaScript and its
   dependencies so they can be tested
 * Adds fixtures for liveblog_settings and liveblog_publisher_settings
 * Fakes out a few things in fixtures.js, so the code runs properly

At the moment, this simple method of bundling is not ideal. It would be better
to write a pre-processor that concatenates the dependencies, or to
switch to using something like RequireJS or Ender to resolve
dependencies properly.
Add NewEntry model

This model will be used for new entries that are to be saved to the
server. The sync function has been overridden so it passes everything
the server should need to process the request.

We turn on Backbone.emulateHTTP here, so all modifying actions will be
sent as HTTP POSTs.
Use underscore's _.throttle instead of the jQuery plugin
Add PublishedEntry model

This will be used for already existing entries, currently it only
supports updates.