Launch SetupActivity in same task to prevent relaunching from recent apps

This branch fixes #1189 (closed) by launching SetupActivity in the same task after deleting the account, and also ensures that PasswordActivity and the activity that launched it are cleaned up if the user presses back from SetupActivity.

briar-android/src/main/java/org/briarproject/briar/android/activity/BriarActivity.java

@@ -62,11 +62,10 @@ public abstract class BriarActivity extends BaseActivity {
 	@Override
 	protected void onActivityResult(int request, int result, Intent data) {
 		super.onActivityResult(request, result, data);
-		if (request == REQUEST_PASSWORD && result == RESULT_OK) {
-			// PasswordActivity finishes when password was entered correctly.
-			// When back button is pressed there, it will bring itself back,
-			// so that we never arrive here with a result that is not OK.
-			briarController.startAndBindService();
+		if (request == REQUEST_PASSWORD) {
+			// The result can be RESULT_CANCELED if there's no account
+			if (result == RESULT_OK) briarController.startAndBindService();
+			else finish();
 		} else if (request == REQUEST_UNLOCK && result != RESULT_OK) {
 			// We arrive here, if the user presses 'back'
 			// in the Keyguard unlock screen, because UnlockActivity finishes.
@@ -81,13 +80,16 @@ public abstract class BriarActivity extends BaseActivity {
 	@Override
 	public void onResume() {
 		super.onResume();
-		if (!briarController.accountSignedIn()) {
+		if (!briarController.accountSignedIn() && !isFinishing()) {
+			// Also check that the activity isn't finishing already.
+			// This is possible if we finished in onActivityResult().
+			// Launching another PasswordActivity would cause a loop.
 			Intent i = new Intent(this, PasswordActivity.class);
 			startActivityForResult(i, REQUEST_PASSWORD);
 		} else if (lockManager.isLocked() && !isFinishing()) {
 			// Also check that the activity isn't finishing already.
-			// This is possible if finishing in onActivityResult().
-			// Failure to do this check would cause an UnlockActivity loop.
+			// This is possible if we finished in onActivityResult().
+			// Lauching another UnlockActivity would cause a loop.
 			Intent i = new Intent(this, UnlockActivity.class);
 			startActivityForResult(i, REQUEST_UNLOCK);
 		} else if (SDK_INT >= 23) {