setup Tor at app start, and config immediately when pref is changed

This adds an Application subclass to get the onCreate() method, which is
called once at the first start up of the app, before any Activity starts.
Tor is configured there to ensure it is setup before anything happens.

This also moves the "Use Tor" pref listener to a more appropriate place.

app/src/main/java/org/schabi/newpipe/App.java

@@ -0,0 +1,32 @@
+package org.schabi.newpipe;
+
+import android.app.Application;
+import android.content.SharedPreferences;
+import android.preference.PreferenceManager;
+
+import info.guardianproject.netcipher.NetCipher;
+import info.guardianproject.netcipher.proxy.OrbotHelper;
+
+public class App extends Application {
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+        // if Orbot is installed, then default to using Tor, the user can still override
+        if (OrbotHelper.requestStartTor(this)) {
+            SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
+            configureTor(prefs.getBoolean(getString(R.string.useTor), true));
+        }
+    }
+
+    /**
+     * Set the proxy settings based on whether Tor should be enabled or not.
+     */
+    static void configureTor(boolean useTor) {
+        if (useTor) {
+            NetCipher.useTor();
+        } else {
+            NetCipher.setProxy(null);
+        }
+    }
+}