Throw exception if account exists when beginning setup.

briar-android/src/main/java/org/briarproject/briar/android/login/SetupActivity.java

@@ -38,6 +38,8 @@ public class SetupActivity extends BaseActivity
 		setContentView(R.layout.activity_fragment_container);
 
 		if (state == null) {
+			if (setupController.accountExists())
+				throw new AssertionError();
 			showInitialFragment(AuthorNameFragment.newInstance());
 		} else {
 			authorName = state.getString(STATE_KEY_AUTHOR_NAME);

briar-android/src/main/java/org/briarproject/briar/android/login/SetupController.java

@@ -3,7 +3,7 @@ package org.briarproject.briar.android.login;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 @NotNullByDefault
-public interface SetupController {
+public interface SetupController extends PasswordController {
 
 	void setSetupActivity(SetupActivity setupActivity);
 
@@ -13,8 +13,6 @@ public interface SetupController {
 
 	void setPassword(String password);
 
-	float estimatePasswordStrength(String password);
-
 	/**
 	 * This should be called after the author name has been set.
 	 */