Truncate all message related tables

[brendanheywood]

https://github.com/catalyst/moodle-local_datacleaner/blob/master/cleaner/core/classes/clean.php#L52

mdl_message_popup mdl_message_processors mdl_message_providers mdl_message_read mdl_message_working

[brendanheywood]

Also change the format of the url cleaner log output:

• [x] remove the estimated seconds left it's junk
• [x] add in the time elapse for just this task
• [x] change both the total elapsed time and the table elapsed time into H:MM:SS
• [ ] use sprintf to align all the columns perfectly

[brendanheywood]

I've assigned @roperto to #25, I'll get him to finish this one off too