* Removed conversion script from selenium IDE export files.
* Created PHPunit XML configuration for test suites
* Introduced tests/selenium_tests/shared_tests for tests shared
  between test suites.
* Introduced new setting 'root_url' in config.ini.php needed for
  running tests (so that selenium knows where to point the browser).
* Created PHPunit bootstrap script to generate global constants
  for tests.
* Created base test class.