Improvements and fixes

Grid meter readings taken through a Phoenix Contact controller no longer arrive with the feed-in direction reversed.

• A Phoenix Contact controller now works out by itself which direction the grid meter counts, and shows no grid values until it is sure.
• "Grid sign convention" in the controller's settings lets you set the direction yourself when the automatic check cannot decide.
• You can add a Huawei data logger without its web login; the plant is read over Modbus TCP, with the login as a fallback.