Use singleton objects for bootstrapping instead of calling
static functions. This way the whole process can be extended
and covered by unit tests much better.

Change-Id: I1d260cfff7a2fc783a709f43fc80de217d941016
Resolves: #38121
Releases: 6.0
Reviewed-on: http://review.typo3.org/12133
Tested-by: Philipp Gampe
Reviewed-by: Philipp Gampe
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn