MDL-45607 events: changed the context passed to the user_profile_viewed event
MDL-45445 events: trivial changes
MDL-45445 events: added missing 'relateduserid' validation
MDL-45445 events: added missing 'other' validation
MDL-45445 events: documented the additional validation
MDL-45445 events: added '(optional)' to event params where applicable