[FEATURE] Monitor peak memory usage

Monitor the peak memory usage during page generation and report if
it exceeds 90% of the memory limit.

Change-Id: Ie0cfed4dce4b2f3e269832a28be7045b972a6867
Resolves: #25836
Reviewed-on: http://review.typo3.org/1507
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog
Tested-by: Thorsten Kahler
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Jigal van Hemert