[UPGRADE] Umbraco 14+ (Bellissima)

[AndyBoot]

Upgrade and migrate the UI and core functionality to the new Bellissima framework.

• Prevent multiple branches
• Solution must contain demo's for each initial major version (1 web project per version)
• Solution must contain a project (or projects) intended for v13 and v14+ and use a shared "core" project
• The versioning of the packages should reflect the Umbraco major version but under the same NuGet package name.
• The versioning of the current release would leap from v1. to v13. to make it easier to identify