encryption: added new backend using cryptography + Fernet encryption.

- This would soon replace the old deprecated one based on pycrypto
- We need a migration for the encryption data

configs/production.ini

@@ -108,6 +108,11 @@ use = egg:rhodecode-enterprise-ce
 ## `SignatureVerificationError` in case of wrong key, or damaged encryption data.
 #rhodecode.encrypted_values.strict = false
 
+## Pick algorithm for encryption. Either fernet (more secure) or aes (default)
+## fernet is safer, and we strongly recommend switching to it.
+## Due to backward compatibility aes is used as default.
+#rhodecode.encrypted_values.algorithm = fernet
+
 ## return gzipped responses from RhodeCode (static files/application)
 gzip_responses = false