[TASK] Restructure bootstrap classes

The scope separation in Bootstrap classes still needs more thoughts
and concepts. For now, the construct is simplified to a simple main
class with most code in it and independent static helper classes
to encapsulate scope specific code.

Change-Id: I3f70ececb876fef8bfce76646f84a86cda439a74
Resolves: #38134
Releases: 6.0
Reviewed-on: http://review.typo3.org/12144
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader