integreen plugin: add first version

- allows to access all InTeGreen REST services in a more friendly way
- allows frontend, call and call parameters to be configured dynamically by input message
integreen plugin - enhance the "params" parameter to accept also JS objects

This is a user-friendly feature, since in that case also the URI-encoding is done by the node.

Example:
{
  "param1": int-value,
  "param2": "str-value",
  ...
}