Create JSON structures from conditions

[sylvainhalle]

The reverse of #22 (i.e. the serialization process). Not necessary at the moment, but could be useful in the future.

[EmilePerron]

As discussed, here is an example.
Assuming a method named toJson() on the AbstractFunction class, the following snippet:

var quantifier = new UniversalQuantifier(
    "$x",
    new FindBySelector("#h2"),
    new ComposedFunction(
        new GreaterThan(),
        new ComposedFunction(new Opacity(), "$x"),
        0.9
    )
);
var json = quantifier.toJson();

console.log(json);

should result in the following serialization (JSON):

{
   "name": "UniversalQuantifier",
   "contents": [
       "$x",
       {
           "name": "FindBySelector",
           "contents": [
               "#h2"
           ]
       },
       {
           "name": "ComposedFunction",
           "contents": [
               {
                   "name": "GreaterThan",
                   "contents": []
               },
               {
                   "name": "ComposedFunction",
                   "contents": [
                       {
                           "name": "Opacity",
                           "contents": []
                       },
                       "$x"
                   ]
               },
               0.9
           ]
       }       
   ]
}