squareBracket Beta 2.0.0

Breaking changes, shit will break and you'll need to fix that.

Updates

• Update twbs/bootstrap requirement from 5.1.2 to 5.1.3 (#78) @dependabot
• Port https://github.com/principia-preservation-project/principia-web-forum to squareBracket (#77) @chaziz94 @rollerozxa
• implement 2012E and later scrap it
• ditch bootstrap for sbnext
• new sounds
• preliminary music support

Full Changelog: beta-1.9...beta-2.0.0