[TASK] Use singleton objects for bootstrapping

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