[TASK] Refactor code to match new structure

- Move language files Resources/Private/Language
- Move CSS to Resources/Public/Css
- Move PageTsConfig to Configuration/TsConfig/Page
- Move all reference to .xml to .xlf

Change-Id: I62a738e81c1685d8f6de7aea746d1c8af343e9d7
Resolves: #46360
Releases: 6.1
Reviewed-on: https://review.typo3.org/18977
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe