BPT #105 Fix get tours for person
BPT #105 Fix get tours for person

- Extend Tourist_model.php with MY_Model to make use of built-in extended functions
- Update Tourist_model.php::get to get the entries for the tourist for a given set of tours.
- update Tourist_model.php::get_missing_tours to use new methods to only show tours the tourist has not been on either as a payer or tourist.

generalludd/tour,generalludd/tour,generalludd/tour