refactor(config): replace RelativeLayout with ConstraintLayout (#1232)

Author: thatfiredev

config/app/src/main/res/layout/activity_main.xml

@@ -1,4 +1,5 @@
-<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
     xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
@@ -12,24 +13,30 @@
         android:id="@+id/icon"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
-        android:layout_centerHorizontal="true"
-        android:layout_marginBottom="16dp"
-        android:src="@drawable/firebase_lockup_400" />
+        android:src="@drawable/firebase_lockup_400"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toTopOf="parent" />
 
     <TextView
         android:id="@+id/welcomeTextView"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_below="@+id/icon"
-        android:layout_centerHorizontal="true"
-        android:text="Welcome..." />
+        android:layout_marginTop="16dp"
+        android:text="Welcome..."
+        app:layout_constraintEnd_toEndOf="@+id/icon"
+        app:layout_constraintStart_toStartOf="@+id/icon"
+        app:layout_constraintTop_toBottomOf="@+id/icon" />
 
     <Button
+        android:id="@+id/fetchButton"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="@string/fetch_remote_welcome_message"
-        android:id="@+id/fetchButton"
-        android:layout_centerVertical="true"
-        android:layout_centerHorizontal="true" />
+        app:layout_constraintBottom_toBottomOf="parent"
+        app:layout_constraintEnd_toEndOf="parent"
+        app:layout_constraintStart_toStartOf="parent"
+        app:layout_constraintTop_toBottomOf="@+id/welcomeTextView" />
 
-</RelativeLayout>
+</androidx.constraintlayout.widget.ConstraintLayout>