Drop support for v8

[bjosttveit]

• Require at least version 9.0.0 of app-lib-dotnet. Ensure this by setting MINIMUM_APPLICATION_VERSION which will show an error if the app is not up to date.
• Remove all code-paths that are in effect if the backend version is not up to date enough (paths where isAtLeastVersion(something) is false), we can assume that all apps are at least these versions when requiring a new major version.
  • Remove unused APIs (appUrlHelper, queries, mutations, etc.)
• Only multi-patch is needed, single-patch can be removed