Change Page.navigate to return main resource response

This patch changes Page.navigate API:
- Page.navigate now resolves to the main page response
- Page.navigate throws errors if there's no main page response,
  e.g. in case of SSL errors, max navigation timeout,
  or invalid url.

This patch also adds httpsServer with a self-signed certificates
for the testing purposes.

Fixes #10.

lib/Page.js

@@ -260,10 +260,26 @@ class Page extends EventEmitter {
   /**
    * @param {string} html
    * @param {!Object=} options
-   * @return {!Promise<boolean>}
+   * @return {!Promise<!Response>}
    */
-  navigate(url, options) {
-    return new Navigator(this._client, url, this._networkManager.httpHeaders().referer, options).navigate();
+  async navigate(url, options) {
+    /** @type {!Map<string, !Response>} */
+    const responses = new Map();
+    const onResponse = response => responses.set(response.url, response);
+    const navigator = new Navigator(this._client, url, this._networkManager.httpHeaders().referer, options);
+
+    try {
+      this._networkManager.on(NetworkManager.Events.Response, onResponse);
+      await navigator.navigate();
+    } catch (e) {
+      this._networkManager.removeListener(NetworkManager.Events.Response, onResponse);
+      throw e;
+    }
+
+    this._networkManager.removeListener(NetworkManager.Events.Response, onResponse);
+    const response = responses.get(this.mainFrame().url());
+    console.assert(response);
+    return response;
   }
 
   /**