feat(locators): Added a By.cssContainingText locator.

This new locator find elements by css selector and inner text in response to the lack of ':contains' selector.

Example: By.cssContainingText('ul .pet', 'Dog') will find all ul children with class 'pet' containing the text 'Dog'.
Merge branch 'by-css-text' of https://github.com/bcaudan/protractor into bcaudan-by-css-text