* Add activity, activityformat, timelimit and submissionattachments to mod_assign_get_assignments
* Add timestarted to mod_assign_get_submissions and mod_assign_get_submission_status
* Add assignmentdata to mod_assign_get_submission_status
* Move mod_assign external helper methods to an external_api child class to be used with modern external classes
* Add start_submission external function
* Create mod_assign child class of externallib_advanced_testcase for shared helper functions
* Add extra logic to get_assignments on whether to provide intro
attachments.
Daniel Ureña