Add "Activity Summary" reports

These reports summarise the other activity reports (except assignments and quizzes).
Adjust "about" dialog to mention LearnTrak
Activity summary report: fix y-axis label

Y-axis label on activity summary report read "Actions on activitysummary".
Merge branch 'learntrak' of https://github.com/pauln/moodle-block_gismo3_uc into learntrak