JSON and XML mutator

[devl00p]

Wapiti needs some new mutators to do the same thing that the current ones (see https://github.com/wapiti-scanner/wapiti/blob/master/wapitiCore/attack/attack.py#L355 ) but for XML and JSON content types.

This means that for example for a given json object:
{"key1": "value1", "key2": ["value2"], "key3": int3}

The following values should be sent when attacking :

{"key1": payload, "key2": ["value2"], "key3": int3}

{"key1": "value1", "key2": [payload], "key3": int3}

{"key1": "value1", "key2": ["value2"], "key3": payload}

I don't think it is necessary to replace all values of a list, let's only overwrite the first element.

We should go into nested dictionaries to overwrite values.

The same should be done for XML too.

[devl00p]

working on the json mutator

[devl00p]

added the JSON mutator: #545

Next step is to integrate it so modules use it correctly

[devl00p]

MR for the ability for modules to inject inside JSON body:

#585