Issue #26 remove old common.js
Issue #26 rename test directory to tests

Since now it will hold actual CasperJS tests.
Issue #26 Add session management, verbose mode and screenshots

This commit adds the follwing features:

* Tests are found at tests directory by default.
* Session managemente and common functions are added for every test.
* Added README file with installation instructions and tips.
* Added examples to the drush casperjs command.
* Added a test for the homepage and a test to create content
  managing sessions.