[!!!][BUGFIX] Accept \Throwable in ExceptionHandlerInterface

Since PHP 7.0 \Exceptions are a subclass of \Throwable, and some PHP
Errors are thrown as \Throwables. So we need to support \Throwables
inside Exception handling.
http://php.net/manual/en/language.errors.php7.php

Resolves: #72117
Releases: master
Change-Id: I4302ab0f91386c4764a1b0e0305cd947987d60eb
Reviewed-on: https://review.typo3.org/45247


Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>