Remodel the Model

- The configuration and crypto model is now entirely independent
of Android classes other than Nullable and TextUtils.
- Model classes are immutable and use builders that enforce the
appropriate optional/required attributes.
- The Android config proxies (for Parcelable and databinding) are
moved to the Android side of the codebase, and are designed to be
safe for two-way databinding. This allows proper observability in
TunnelDetailFragment.
- Various robustness fixes and documentation updates to helper classes.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java

@@ -16,7 +16,6 @@ import android.view.ViewGroup;
 import com.wireguard.android.R;
 import com.wireguard.android.databinding.TunnelDetailFragmentBinding;
 import com.wireguard.android.model.Tunnel;
-import com.wireguard.config.Config;
 
 /**
  * Fragment that shows details about a specific tunnel.
@@ -25,12 +24,6 @@ import com.wireguard.config.Config;
 public class TunnelDetailFragment extends BaseFragment {
     @Nullable private TunnelDetailFragmentBinding binding;
 
-    private void onConfigLoaded(final String name, final Config config) {
-        if (binding != null) {
-            binding.setConfig(new Config.Observable(config, name));
-        }
-    }
-
     @Override
     public void onCreate(@Nullable final Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
@@ -65,7 +58,7 @@ public class TunnelDetailFragment extends BaseFragment {
         if (newTunnel == null)
             binding.setConfig(null);
         else
-            newTunnel.getConfigAsync().thenAccept(a -> onConfigLoaded(newTunnel.getName(), a));
+            newTunnel.getConfigAsync().thenAccept(binding::setConfig);
     }
 
     @Override