Aperture: Properly center bottom buttons

Change-Id: I7489d6766df8161471cd9e5665c59bae46d14360
diff --git a/app/src/main/res/layout/activity_main.xml b/app/src/main/res/layout/activity_main.xml
index 8e5096e..32c136b 100644
--- a/app/src/main/res/layout/activity_main.xml
+++ b/app/src/main/res/layout/activity_main.xml
@@ -277,9 +277,12 @@
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:contentDescription="@string/photo_mode_button_description"
+            android:padding="0dp"
             android:text="@string/selector_photo"
+            app:iconPadding="0dp"
             app:layout_constraintBottom_toBottomOf="parent"
             app:layout_constraintEnd_toStartOf="@+id/videoModeButton"
+            app:layout_constraintHorizontal_bias="0.5"
             app:layout_constraintStart_toStartOf="parent"
             app:layout_constraintTop_toTopOf="parent" />
 
@@ -289,9 +292,12 @@
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:contentDescription="@string/video_mode_button_description"
+            android:padding="0dp"
             android:text="@string/select_video"
+            app:iconPadding="0dp"
             app:layout_constraintBottom_toBottomOf="parent"
             app:layout_constraintEnd_toStartOf="@+id/qrModeButton"
+            app:layout_constraintHorizontal_bias="0.5"
             app:layout_constraintStart_toEndOf="@+id/photoModeButton"
             app:layout_constraintTop_toTopOf="parent" />
 
@@ -301,9 +307,12 @@
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:contentDescription="@string/qr_mode_button_description"
+            android:padding="0dp"
             android:text="@string/select_scan"
+            app:iconPadding="0dp"
             app:layout_constraintBottom_toBottomOf="parent"
             app:layout_constraintEnd_toEndOf="parent"
+            app:layout_constraintHorizontal_bias="0.5"
             app:layout_constraintStart_toEndOf="@+id/videoModeButton"
             app:layout_constraintTop_toTopOf="parent" />
     </androidx.constraintlayout.widget.ConstraintLayout>