[TASK] Invalidate autoloader cache in em

The autoloader cache should be invalidated by the extension manager
if installing new or removing old extension from extension list to
force a recalculation of available classes on next access.

Change-Id: I485dc62aa2d3644136392b7608c77a11cf408332
Resolves: #28219
Related: #28063
Related: #28186
Related: #28187
Reviewed-on: http://review.typo3.org/3339
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers