MDL-40051 core_event: created an abstract class for viewing reports
MDL-40051 tool_capability: replaced add_to_log call with an event
MDL-40051 report_questioninstances: replaced add_to_log call with an event
MDL-40051 mnet: replaced add_to_log calls with events
MDL-40051 core_lib: replaced add_to_log calls related to file uploads with events
MDL-40051 core_lib: replaced add_to_log call when failing to send email with an event