To speed up filling out header parameters in Rest Connection and avoid typos, it would be good to have already predefined list of known headers, e.g. Accept, Accept-Encoding, Authorization, Content-Type etc. To make it more flexible we can remain current possibility to enter some header which is not in the predefined list.
For Content-Type header we could also add a predefined list of supported in Rest Connection content types: application/xml and application/json.
