Remove window.dataExplorerPlatform (#279)

More cleanup for #253 
- Remove window.dataExplorerPlatform
- Remove explorer factories

src/TokenProviders/TokenProviderFactory.ts

@@ -1,17 +1,17 @@
+import { configContext, Platform } from "../ConfigContext";
 import * as ViewModels from "../Contracts/ViewModels";
-import { PlatformType } from "../PlatformType";
 import { PortalTokenProvider } from "./PortalTokenProvider";
 
 export class TokenProviderFactory {
   private constructor() {}
 
   public static create(): ViewModels.TokenProvider {
-    const platformType = window.dataExplorerPlatform;
+    const platformType = configContext.platform;
     switch (platformType) {
-      case PlatformType.Portal:
-      case PlatformType.Hosted:
+      case Platform.Portal:
+      case Platform.Hosted:
         return new PortalTokenProvider();
-      case PlatformType.Emulator:
+      case Platform.Emulator:
       default:
         // should never get into this state
         throw new Error(`Unknown platform ${platformType}`);