[!!!][TASK] Make TimeTracker a singleton

By declaring the TimeTracker class as singleton, there is no
need anymore for $GLOBALS['TT'].

Change-Id: I412fbdcbd2c60dcaae4dc592bea48a7d059f7e95
Resolves: #73504
Releases: master
Reviewed-on: https://review.typo3.org/46520


Reviewed-by: Michiel Roos <michiel@maxserv.com>
Tested-by: Michiel Roos <michiel@maxserv.com>
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>