Add 'Azure' category (#8)

* Add 'Azure' category

* Update README.md

* Fix typo

* Track LoadDeviceTree event when it is successfully

README.md

@@ -25,7 +25,7 @@ Interact with Azure IoT Hub, IoT Device Management, IoT Hub Code Snippets.
 
 ![Click Device Explorer](https://github.com/formulahendry/vscode-azure-iot-toolkit/raw/master/images/device-explorer-click.png)
 
-2. If you have not set Iot Hub Connection String before, an input box will pop up, then enter your Iot Hub Connection String (It is one-time configuration).
+2. If you have not set Iot Hub Connection String before, an input box will pop up, then enter your Iot Hub Connection String (It is one-time configuration, and please make sure it is **Iot Hub Connection String** not **Device Connection String**).
 
 ![Enter Connection String](https://github.com/formulahendry/vscode-azure-iot-toolkit/raw/master/images/enter-connection-string.png)
 

package.json

@@ -9,7 +9,7 @@
     "vscode": "^1.13.0"
   },
   "categories": [
-    "Other",
+    "Azure",
     "Languages",
     "Snippets"
   ],

src/deviceTree.ts

@@ -29,7 +29,6 @@ export class DeviceTree implements vscode.TreeDataProvider<DeviceItem> {
             return;
         }
 
-        TelemetryClient.sendEvent(Constants.IoTHubAILoadDeviceTreeEvent);
         let registry = iothub.Registry.fromConnectionString(iotHubConnectionString);
         let devices = [];
         let hostName = Utility.getHostName(iotHubConnectionString);
@@ -39,6 +38,7 @@ export class DeviceTree implements vscode.TreeDataProvider<DeviceItem> {
                 if (err) {
                     reject(`[Failed to list IoT Hub devices] ${err.message}`);
                 } else {
+                    TelemetryClient.sendEvent(Constants.IoTHubAILoadDeviceTreeEvent);
                     deviceList.forEach((device, index) => {
                         let image = device.connectionState.toString() === "Connected" ? "device-on.png" : "device-off.png";
                         devices.push(new DeviceItem(device.deviceId,