Get current Work item data in VSTS Extension - azure-devops

Question

I am want to create a VSTS Extension for TFS 2015 Update 3 and I want to start slow. I want to create a custom action that shows the Id and the Title of the current Work Item in one pop up window.
I have been reading the tutorials but I still don't get it.
I used this example from GitHub:
var showPropertiesMenuProvider = (function () {
"use strict";
return {
showPropertiesInDialog: function(properties, title) {
VSS.getService("ms.vss-web.dialog-service").then(function (dialogSvc) {
var extInfo = VSS.getExtensionContext();
var contibution = VSS.getContribution();
var dialogOptions = {
title: title || "Properties",
width: 800,
height: 600,
buttons: null
};
var contributionConfig = {
properties: properties
};
dialogSvc.openDialog(extInfo.publisherId + "." + extInfo.extensionId + "." + "contextForm", dialogOptions, contributionConfig);
});
},
execute: function(actionContext) {
this.showPropertiesInDialog(actionContext);
}
};
}());
VSS.register("showProperties", function (context) {
return showPropertiesMenuProvider;
});
which gives me a lot of information but I still can't extract the data I need.
Any ideas?
Thanks in advance!