Migrate to the new multisrc structure

[stevenyomi]

• Migrate
  • HeanCms multisrc migration #278
  • lib-multisrc migration (draft for review) #1200
  • Add build files for lib-multisrc migration #1228
  • Migrate to lib-multisrc #1237
• Rename projects Address some gradle warnings #259 (comment)
  • Rename projects to path names #1240
• Enforce PR build check on merge (after existing PRs got merged)
• Documentation
• Reuse baseUrl in source code (depends on Lib to help add configurable base URL #1617)

General/long-term todos

• Partial build in CI and PR build checks
• Scan scripts and audit scripts
• Custom audit rules enforced with ktlint
• Rename namespace (depends on Lib to help add configurable base URL #1617)