make invite strings plural

fixes #4388
Closes #4389

// FREEBIE

res/values/strings.xml

@@ -280,8 +280,14 @@
     <string name="InviteActivity_heart_content_description">Heart</string>
     <string name="InviteActivity_invitations_sent">Invitations sent!</string>
     <string name="InviteActivity_invite_to_signal">Invite to Signal</string>
-    <string name="InviteActivity_send_to_friends">SEND TO %1$s FRIEND(S)</string>
-    <string name="InviteActivity_send_sms_invites">Send %1$s SMS invite(s)?</string>
+    <plurals name="InviteActivity_send_to_friends">
+        <item quantity="one">SEND TO ONE FRIEND</item>
+        <item quantity="other">SEND TO %d FRIENDS</item>
+    </plurals>
+    <plurals name="InviteActivity_send_sms_invites">
+        <item quantity="one">Send one SMS invite?</item>
+        <item quantity="other">Send %d SMS invites?</item>
+    </plurals>
     <string name="InviteActivity_lets_switch_to_signal">Let\'s switch to Signal: %1$s</string>
     <string name="InviteActivity_no_app_to_share_to">It looks like you don\'t have any apps to share to.</string>
     <string name="InviteActivity_friends_dont_let_friends_text_unencrypted">Friends don\'t let friends chat unencrypted.</string>

src/org/thoughtcrime/securesms/InviteActivity.java

@@ -115,7 +115,9 @@ public class InviteActivity extends PassphraseRequiredActionBarActivity implemen
   }
 
   private void updateSmsButtonText() {
-    smsSendButton.setText(getString(R.string.InviteActivity_send_to_friends, contactsFragment.getSelectedContacts().size()));
+    smsSendButton.setText(getResources().getQuantityString(R.plurals.InviteActivity_send_to_friends,
+                                                           contactsFragment.getSelectedContacts().size(),
+                                                           contactsFragment.getSelectedContacts().size()));
     smsSendButton.setEnabled(!contactsFragment.getSelectedContacts().isEmpty());
   }
 
@@ -166,7 +168,9 @@ public class InviteActivity extends PassphraseRequiredActionBarActivity implemen
     @Override
     public void onClick(View v) {
       new AlertDialog.Builder(InviteActivity.this)
-          .setTitle(getString(R.string.InviteActivity_send_sms_invites, contactsFragment.getSelectedContacts().size()))
+          .setTitle(getResources().getQuantityString(R.plurals.InviteActivity_send_sms_invites,
+                                                     contactsFragment.getSelectedContacts().size(),
+                                                     contactsFragment.getSelectedContacts().size()))
           .setMessage(inviteText.getText().toString())
           .setPositiveButton(R.string.yes, new DialogInterface.OnClickListener() {
             @Override public void onClick(DialogInterface dialog, int which) {