Added functionality to answering

Now, users using an external keyboard can press 'enter' to submit their
answer. Also, delayed clearing the answering textbox until the next
question is displayed.

app/src/main/java/com/noprestige/kanaquiz/MainQuiz.java

@@ -53,7 +53,7 @@ protected void onCreate(Bundle savedInstanceState)
             {
                 public boolean onEditorAction(TextView v, int actionId, KeyEvent event)
                 {
-                    if ((actionId == EditorInfo.IME_ACTION_GO) && btnSubmit.isEnabled())
+                    if (((actionId == EditorInfo.IME_ACTION_GO) || (actionId == EditorInfo.IME_NULL)) && btnSubmit.isEnabled())
                     {
                         submitAnswer();
                         return true;
@@ -141,7 +141,7 @@ private void checkAnswer()
             lblResponse.setTextColor(ContextCompat.getColor(this, R.color.incorrect));
         }
         totalQuestions++;
-        txtAnswer.setText("");
+        txtAnswer.setEnabled(false);
         btnSubmit.setEnabled(false);
     }