Revert AndroidManifest.xml package name change

Changing this requires changing the import path of the generated R file, which
will unnecessarily affect most of the code. R is built in a package based on
the AndroidManifest.xml package name, whereas the final app package name is
overridden in app/build.gradle for free and donate versions.

app/src/main/AndroidManifest.xml

 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
-    package="net.i2p.android"
+    package="net.i2p.android.router"
     android:installLocation="auto"
     android:versionCode="4745216"
     android:versionName="0.9.13-0_b0-API9">