MDL-46352 core_lib: group_picture renderable + renderer
MDL-45862 mod_forum: Start of moving to renderables.
MDL-45862 mod_forum: More renderable joy
MDL-45862 mod_forum: Convert forum_print_posts-nested
MDL-45862 mod_forum: Convert all uses to forum_display_post for the moment
MDL-45862 mod_forum: Big change to make renderables with children
MDL-45862 mod_forum: Tidy up message separation
MDL-45862 mod_forum: More semantic HTML
MDL-46285 core_renderers: optionally hide user_picture from screen readers
MDL-45862 mod_forum: attachments renderer, byline renderer, group_picture support, hidden posts
MDL-45862: post commands renderable