[BUGFIX] Install new system extensions during upgrade process fails

If you try to update your system from 4.7 to current master the second
step "Install System Extensions" fails because of missing extensionmanager
tables.

So we have to push up the initialisation process from EM and adopt
it to include ext_tables.sql as well (at the moment only the file
ext_tables_static+adt.sql is processed).

Change-Id: I5cd4616e5bccd06e86fa3ae4fbde8a083afa428f
Fixes: #42616
Releases: 6.0
Reviewed-on: http://review.typo3.org/16153
Reviewed-by: Mattias Nilsson
Reviewed-by: Wouter Wolters
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel