Enable to see where and what you have drawn

If an ending event is detected, the drive will take a screenshot,
and sends it back to the app.
The client will than put it as its background image.

Android app changes:

* Added write permission to the app.

* Added method to get the canvas object from anywhere.

* Added network server to retrieve the image.

* Added method to send a atop motion event signal, which is needed to
  trigger the driver to send a new screenshot.

* Changed commit to apply because it is deprecated.

* The template image will now always fit the screen. (Removed TODO)

* Commented out grid pattern.

* Updated gradle version.

Driver changes:

* Included a lot of new library's, not sure if every is needed right now.

* Added type definition for some structures.

* Added function to sleep in ms.

* Added function for the screenshot sending thread.

* Changed recv to recvfrom to get the IP of the android device in order
  to send back the screenshot.

TODO:

* Show the cursor path in the app.

* Sort out driver library's.

* Add the picture path to the option dialog.

* Create the screenshot in /tmp with a more suitable name.

* Sort functions that are not needed anymore.

app-android/app/src/main/java/at/bitfire/gfxtablet/CanvasView.java

@@ -56,8 +56,8 @@ public class CanvasView extends View implements SharedPreferences.OnSharedPrefer
     protected void setBackground() {
         if (settings.getBoolean(SettingsActivity.KEY_DARK_CANVAS, false))
             setBackgroundColor(Color.BLACK);
-        else
-            setBackgroundResource(R.drawable.bg_grid_pattern);
+        //else
+            //setBackgroundResource(R.drawable.bg_grid_pattern); //<-- Add this as option?
     }
 
     protected void setInputMethods() {