Improve checklist_print_overview()

1. Add a new global setting - show only updateable checklists
2. If that setting is enabled then CHECKLIST_MARKING_TEACHER checklists
will not be shown in 'my moodle'
3. If that setting is enabled and the user does not have the capability
'updateown', then skip that checklist
4. 'CHECKLIST_MARKING_BOTH' checklists should also be hidden, as
students cannot affect the progress bar, only teachers can update the
progress bar.
5. Site Admin's will not see any checklist notices
Merge pull request #28 from Syxton/improve_overview

Improve checklist_print_overview()