chore(): optimize CordovaProperty and InstanceProperty decorators (#635)

* chore(): optimize InstanceProperty wrapper

* chore(): optimize CordovaProperty wrapper

* tslint'

* fix decorators

src/plugins/device.ts

@@ -1,11 +1,12 @@
 import { CordovaProperty, Plugin } from './plugin';
 
 
-declare var window: {
-  device: Device
-};
+declare var window: any;
 
-export interface Device {
+/**
+ * @private
+ */
+export interface IDevice {
   /** Get the version of Cordova running on the device. */
   cordova: string;
   /**
@@ -54,6 +55,6 @@ export class Device {
    * @returns {Device} The device object.
    */
   @CordovaProperty
-  static get device(): Device { return window.device; }
+  static device: IDevice;
 
 }