Total time spend on tasks and breakdown

[brendanheywood]

This may come from excimer or somewhere else TBA

We want a few metrics:

• [ ] total time spent on tasks, probably per day (imagine this would be 10 days worth of run time on some large sites)
• [ ] breakdown by task type

[brendanheywood]

Closing see https://github.com/catalyst/moodle-tool_excimer/issues/250