Remove container class for intro slides

Even with passing a bundle with the layout ID sometimes
some users will encounter a situation where the _layout
variable is null. To avoid further issues, creating a
class for each intro slide, so the layout is encoded
into the class itself.

app/src/main/java/protect/card_locker/MainActivity.java

@@ -29,6 +29,8 @@ import com.google.common.collect.ImmutableMap;
 import java.util.Calendar;
 import java.util.Map;
 
+import protect.card_locker.intro.IntroActivity;
+
 public class MainActivity extends AppCompatActivity
 {
     private static final String TAG = "LoyaltyCardLocker";