Merge pull request #9754 from owncloud/enc_support_aes_256

[encryption] support aes 256

diff --cc apps/files_encryption/hooks/hooks.php
Simple merge

diff --cc apps/files_encryption/lib/helper.php
Simple merge

diff --cc apps/files_encryption/lib/session.php
Simple merge

diff --cc apps/files_encryption/lib/util.php
Simple merge

diff --cc apps/files_encryption/tests/util.php
Simple merge