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
MDL-40123 behat: Show all of form's elements changes.

* Avoid waiting until Show more... links appears if we
  already waited.
* Use collapse/expand button rather than clicking on
  each of the form's fieldsets.