Change: javascript updates

 * replaced " with ' so we don't have to parse/escape js
 * put inline js into an external file
Bugfix: switch back to window

 * use window method when `null` is given
 * switches back to the window automatically
Bugfix: drag and drop

 * was missing perform() to ... well, perform all actions
Enhancement: put javascript into external file
Change: refactored WebDriver creation

 * moved heavy lifting from CTOR into start()
 * to unify setup process
 * introduced Selenium2Driver::$wdHost and Selenium2Driver::$implicitWait
Bugfix: make testAdvancedForm() run
Bugfix: fix find() to make last tests pass

 * had to incorporate findElements() to match multiple, not just one
Enhancement: document testing (with PHP 5.4+)