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/MockInstallablePackageManager.java

@@ -0,0 +1,59 @@
+package mock;
+
+import android.content.pm.ApplicationInfo;
+import android.content.pm.PackageInfo;
+import android.test.mock.MockPackageManager;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+
+public class MockInstallablePackageManager extends MockPackageManager {
+
+    private List<PackageInfo> info = new ArrayList<>();
+
+    @Override
+    public List<PackageInfo> getInstalledPackages(int flags) {
+        return info;
+    }
+
+    @Override
+    public PackageInfo getPackageInfo(String id, int flags) {
+        for (PackageInfo i : info) {
+            if (i.packageName.equals(id)) {
+                return i;
+            }
+        }
+        return null;
+    }
+
+    public void install(String id, int version, String versionName) {
+        PackageInfo existing = getPackageInfo(id, 0);
+        if (existing != null) {
+            existing.versionCode = version;
+            existing.versionName = versionName;
+        } else {
+            PackageInfo p = new PackageInfo();
+            p.packageName = id;
+            p.versionCode = version;
+            p.versionName = versionName;
+            info.add(p);
+        }
+    }
+
+    @Override
+    public ApplicationInfo getApplicationInfo(String packageName, int flags) throws NameNotFoundException {
+        return new MockApplicationInfo(getPackageInfo(packageName, 0));
+    }
+
+    public void remove(String id) {
+        for (Iterator<PackageInfo> it = info.iterator(); it.hasNext();) {
+            PackageInfo info = it.next();
+            if (info.packageName.equals(id)) {
+                it.remove();
+                return;
+            }
+        }
+    }
+
+}