Extract code from init.php and put it to methods in Bootstrap.php.
Additionally, cli_dispatch and install/index.php do not require
init.php anymore and have a uncoupled bootstrap now.

There is still room for improvement,
this patch is just another intermediate step.

Change-Id: I5c6d84b8acb7760c8a77f192b2b5ba063b417b0d
Resolves: #37130
Releases: 6.0
Reviewed-on: http://review.typo3.org/11153
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel
Reviewed-by: Philipp Gampe
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn