Page Versions

[JuKu]

Add a VCS for pages.

For diff viewing maybe we can use this javascript tool: https://diff2html.xyz/

[PascalReintjens]

Each time someone edits a page, this should result in a new page version.

• If the page is already published, this new version should not immediately go live, instead it lands in a version history. A editor can look at any version in the version history and compare it via a diff view with the currently published version and set it for publication
• There are two tables: pages and page_versions. A not yet published page is initially only available in page_versions. By publishing a page version, this page version gets copied over to pages. (so that not published pages don't slow down the query) In case a page gets updated with a newer page version, the old page version in pages gets overwritten by the new version

[JuKu]

@PascalReintjens To support reverts we should also add a HEAD versionID, like gitub. Else editing will be always based on latest version.