Ability to inject plugins

[Tsilo]

in order to pass preset/plugins we need to add checking in jsTplString so it can push new functions to array

for (var attrname in customOptions) {
    if(attrname == "presets" || attrname == "plugins"){
      swaggerOptions[attrname].push(customOptions[attrname]);
    }else{
      swaggerOptions[attrname] = customOptions[attrname];
    }
  }

here's inject example

var SwaggerHmacAuth = function (system) {
  return {
    statePlugins: {
      spec: {
        wrapActions: {
          setMutatedRequest: (oriAction, system) => (str) => {
            // here, you can hand the value to some function that exists outside of Swagger UI
            console.log('Here is my API definition', str, oriAction, system);
            return oriAction(str); // don't forget! otherwise, Swagger UI won't update
          },
        },
      },
    },
  };
};
let swaggerOptions = {
  presets: [SwaggerHmacAuth],
};