user interface to allow user to decrypt all his files once the encryption app was disabled

Conflicts:
	settings/templates/personal.php
add ajax call to decrypt all files

Conflicts:
	apps/files_encryption/lib/crypt.php
register decrypt all route
add decryptall.php
working decrypt files method
improved error handling
use path relative to data/
only write keyfiles if it was a new file, otherwise nothing changed
check if app is enabled
encrypt/decrypt file versions
only show decrypt all files option if encrypted files are available
adapt unit tests to the modified stream wrapper
remove unused method, the right one is in util.php
handle error if we can't handle the given path
we need to use the path relative to data/
fixing some unit tests
fix searchUsers() call in group.php
this test works locally, let's see what out build server says...
this hopefully fixes testRecoveryForUser(), works locally
for now I disabled testRecoveryFile(), no idea why jenkins deletes complete folders... Works nicely in the real world
use OC\Files\View to read encrypted file, so that it also works with external storages