move main project files into standard gradle/Android Studio layout

This makes it a lot easier to setup all the testing stuff.  Mostly,
I'm tired of fighting Android Studio's fragility, so I want to remove
as much non-standardness as possible in the hopes of improving that
situation.

closes #534 https://gitlab.com/fdroid/fdroidclient/issues/534

app/src/androidTest/java/mock/MockApplicationInfo.java

@@ -0,0 +1,19 @@
+package mock;
+
+import android.content.pm.ApplicationInfo;
+import android.content.pm.PackageInfo;
+import android.content.pm.PackageManager;
+
+public class MockApplicationInfo extends ApplicationInfo {
+
+    private final PackageInfo info;
+
+    public MockApplicationInfo(PackageInfo info) {
+        this.info = info;
+    }
+
+    @Override
+    public CharSequence loadLabel(PackageManager pm) {
+        return "Mock app: " + info.packageName;
+    }
+}