Fix namespace of files_encryption classes and autoload them

apps/files_encryption/appinfo/app.php

apps/files_encryption/exception/encryptionexception.php

apps/files_encryption/exception/multikeydecryptexception.php

apps/files_encryption/exception/multikeyencryptexception.php

apps/files_encryption/lib/capabilities.php

apps/files_encryption/lib/crypt.php

apps/files_encryption/lib/helper.php

apps/files_encryption/lib/hooks.php

apps/files_encryption/lib/keymanager.php

apps/files_encryption/lib/proxy.php

apps/files_encryption/lib/session.php

apps/files_encryption/lib/stream.php

apps/files_encryption/lib/util.php