Merge pull request #11561 from owncloud/stable6-enc-webdavcopywithencryptionfix

[stable6] add support for webdav copy to the encryption and versions app
Fix share key finding algorithm in various cases

Instead of inaccurate pattern matching, use the list of users who we
know have access to the file to build the list of share keys.

This covers the following cases:

- Move/copy files into a subfolder within a share
- Unsharing from a user
- Deleting files directlry / moving share keys to trashbin

Conflicts:
	apps/files_encryption/lib/keymanager.php
	apps/files_encryption/tests/hooks.php
	apps/files_encryption/tests/keymanager.php
	apps/files_encryption/tests/trashbin.php
Removed broken/unneeded fixFileSize

fixFileSize is not needed as the target file will already have the
correct unencrypted size after renaming