Add request date and time to context

[JakubTesarek]

Add current date and time to context.

[JakubTesarek]

There's a problem with the jsonpath-ng library which doesn't allow to concatenate variables using +. This means that user can't create their own datetime like this:

{"$ref": "$.time.H + ':' $.time.M"}

Context has to either contain pre-formated datetime or we have to fix the bug in jsonpath library.