MDL-41101 mod_assign: replaced 'view submit assignment form' add_to_log call with an event
MDL-41101 mod_assign: replaced 'view' add_to_log call for the reveal identities confirmation page with an event
MDL-41101 mod_assign: replaced 'submission statement accepted' add_to_log call with an event

Also removed unnecessary add_to_log call.
MDL-41101 mod_assign: replaced 'view confirm submit assignment form' add_to_log call with an event
MDL-41101 mod_assign: replaced 'view' add_to_log call for the submission status page with an event
MDL-41101 mod_assign: replaced 'view batch set marking workflow state' add_to_log call with an event
MDL-41101 mod_assign: replaced 'view batch set marker allocation' add_to_log call with an event
MDL-41101 mod_assign: replaced 'grade submission' add_to_log call with an event
MDL-41101 mod_assign: replaced 'save grading feedback' add_to_log call with an event