MDL-15452 - Put the OU quiz navigation improvements into the Moodle codebase - quite...

MDL-15452 - Put the OU quiz navigation improvements into the Moodle codebase - quite a lot of progress, sorry I am committing this as a big lump, but it took me a while to get the code back to a working state.

MDL-15537 - create oo attemptlib.php to hold shared code between attempt, summary and review.php
MDL-15541 - Refactor starting a new attempt into a new file startattempt.php
MDL-15538 - Rework attempt.php to use attemptlib.php