MDL-40052 events: Add a base class for content view
MDL-40052 events: Add content view events for report_log
MDL-40052 events: Add content view events for report_loglive
MDL-40052 events: Add content view events for report_outline
MDL-40052 events: Add content view events for report_participation
MDL-40052 events: Add content view events for report_stats
MDL-40052 events: Add get_url() api to various report content_viewed classes