Merge pull request #4691 from owncloud/encryption_improved_error_messages_4617

apps/files/index.php

apps/files/js/files.js

apps/files/templates/index.php

apps/files_encryption/ajax/updatePrivateKeyPassword.php

apps/files_encryption/appinfo/app.php

apps/files_encryption/appinfo/version

apps/files_encryption/files/error.php

apps/files_encryption/hooks/hooks.php

apps/files_encryption/lib/helper.php

apps/files_encryption/lib/session.php

apps/files_encryption/lib/stream.php

apps/files_encryption/lib/util.php

apps/files_encryption/settings-personal.php

apps/files_encryption/templates/invalid_private_key.php

apps/files_encryption/templates/settings-personal.php