MDL-39635 behat: Fixing line breaks

Not supported by Windows OSs.
MDL-39635 behat: Replacing hardcoded language strings

Using get_string() instead.
MDL-39635 behat: XPath cleanups

- Escaping steps arguments redirected to other steps
- Adding normalized-space() in all contains() assertions
- General xpaths review
- Convering provided xpath text strings to xpath literals
  to avoid problems with arguments containing both single
  quotes and double quotes