No default Content-Type for requests

[EvaSDK]

Results in the following messages in logs when some POST requests are generated when opening an URL:

content-type missing in HTTP POST, defaulting to application/x-www-form-urlencoded. Use QNetworkRequest::setHeader() to fix this problem.

A default must be set as explained here:
https://forum.qt.io/topic/17681/solved-content-type-missing-in-http-post-defaulting-to-application-octet-stream/2