[TASK] Versions: Move backend template to extension context

Most html templates in backend are used in one extension only.
Those templates should be held in extension context to reduce
dependencies.

Creates extbase/flow directory structures.

Change-Id: Ic65c85492898bdd325a642c5c5d90b2b6b7f85bf
Fixes: #47794
Releases: 6.2
Reviewed-on: https://review.typo3.org/20385
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn