#49 Add a "Groups - by Duration" listing

! meta: bug ! meta: bug (user-facing) ! meta: code cleanup ! meta: enhancement ! meta: localization ! meta: needs discussion ! meta: new feature/page ! meta: repo structure/content ! meta: tech debt build: cross-OS support build: performance build: thumbnail generation build: top-level steps data: content tags/text data: format data: processing page part: chronology links page part: footer page part: meta/headers page part: nav bar page part: random links page part: release info page: generation page: layout/design thing: albums thing: art tags thing: artists thing: flashes thing: groups thing: homepage layout thing: listings thing: news entries thing: static pages thing: tracks thing: wiki info