Prepare basic unit tests for civicrm-wordpress

For CiviCRM 4.6, we're expecting to use Christian Wach's rewrite of the civicrm-wordpress integration code. Part of the motivation is that several of the integration points behaved weirdly in the old integration-code (e.g. JS resources might load on one screen but fail to load on another screen).

The idea with this ticket is to capture some of those cases in an automated test for civicrm-wordpress. Some particular proposals for automated tests:

1. A test in which some WordPress code uses add_action() to register to for a Civi hook – and which the hook actually fires. Ensure that the callback is called as expected.
2. A test in which a user views a core CiviCRM page through the WP backend. Ensure that JS/CSS files/settings load
3. A test in which a user views a core CiviCRM page through the WP frontend. Ensure that JS/CSS files/settings load
4. A test in which a user views a WP page with a CiviCRM shortcode. Ensure that JS/CSS files/settings load