v5.1-r2

What's Changed

• Group letters by date by @TamaroWalter in #29
• Replace old bootstrap classes by @TamaroWalter in #31
• Restructure js by @TamaroWalter in #32
• Bugfix: letter group does not expands with "show more" button by @TamaroWalter in #34

Full Changelog: v5.1-r1...v5.1-r2