DownloadWorker: simplify & improve code [1/2]

TODO:
- Reduce notification frequency, create too many notifications resulting in notification actions being inaccesible.
- Its a bad practive to bombard system with notification redraws

app/src/main/AndroidManifest.xml

@@ -160,6 +160,11 @@
             android:name=".data.receiver.InstallerStatusReceiver"
             android:exported="false" />
 
+        <!-- Cancel Download Receiver-->
+        <receiver
+            android:name=".data.receiver.DownloadCancelReceiver"
+            android:exported="false" />
+
         <!-- SessionInstaller (as device owner) -->
         <receiver
             android:name=".data.receiver.DeviceOwnerReceiver"