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 https://github.com/hackair-project/hackAir-Arduino/pull/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 https://github.com/hackair-project/hackAir-Arduino/issues/13)
• The humidity correction is only done when the sensor measurement and the DHT humidity measurements were successful. (solving https://github.com/hackair-project/hackAir-Arduino/issues/14)