Add support for passing JSON string into port

[TomCC7]

Describe the bug
Currently when setting the port value to be a json string from xml files, the parser will recognize everything in the bracket "{}" as a variable and produce wrong result. This happens even if double bracket is used to escape the bracketing.

How to Reproduce
Create a node that takes a string as argument and in the xml file:

<Node settings='{{"a": 0.8, "b": 0.7}}'/>