Replace add_to_log with an event trigger - tag

Test 1 Run "vendor/bin/phpunit tag/tests/events_test.php" and ensure all passes. Test 2 Visit <yoursite>/admin/settings.php?section=managelogging and enable 'Standard log'. Visit <yoursite>/admin/settings.php?section=optionalsubsystems and check 'Enable tags functionality' and 'Save changes' - if not already enabled. Visit <yoursite>/admin/settings.php?section=blocksettingtags and check 'Show course tags' and 'Save changes' - if not already enabled. Open up another tab and go to <yoursite>/report/log/index.php and select the 'Standard log'. View this tab whenever the testing instructions say to view any new events that were added. Visit a course. Add the 'Tags' block. Add a tag to the course (remember the name). Check the log report and ensure there is a 'Tag created', 'Tag updated' (the reason there is a 'Tag updated' event is because once the tag has been created the type is then set - I don't know why the API was designed this way but it is out of the scope of this issue) and then a 'Item tagged' event. Add a wiki to the course. Create the first page and add the same tag you used earlier to the page. Check that there is an 'Item tagged' event in the log report. Now completely remove the wiki instance. Check that there is an 'Item untagged' event in the log report. Go back to the course page and select "Edit my tags". Remove the tag. Check that there is an 'Item untagged' and a 'Tag deleted' event.