[!!!][TASK] Restructure lowlevel commands and documentation

The HOWTO cleanup TYPO3 installations document is moved to a README.md
file. The shell scripts for checking and cleaning tasks have been
removed and have been documented in the README.md.

Resolves: #67946
Releases: master
Change-Id: I5de544a9e3508ba2ea946d2fcbe5e47fdf112b29
Reviewed-on: http://review.typo3.org/40948


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>