Adding error handling and retry mechanism for Wemos.ino sketch

[dl1com]

This Pull Request consists of three improvements:

• As already stated for the WifiShield Sketch in on error, retry getting valid data from sensor #12, a time-based retry mechanism for the sensor measurement has been implemented.
• The error and tamper fields of the data struct are actually written into the JSON String (solving [Wemos.ino] Send error and tamper fields to server #13)
• The humidity correction is only done when the sensor measurement and the DHT humidity measurements were successful. (solving [Wemos.ino] Failing DHT measurement not handled #14)