accountCreation: put titles at center

Change-Id: I92eac4831bdb9e9ce78cc888bb365d990af83401

ring-android/app/src/main/res/layout/frag_acc_jami_connect.xml

@@ -51,6 +51,7 @@
             android:layout_alignParentTop="true"
             android:layout_margin="@dimen/text_margin"
             android:gravity="center"
+            android:layout_centerHorizontal="true"
             android:text="@string/account_connect_server_button"
             android:textAppearance="@style/TextAppearance.MaterialComponents.Headline5"
             android:textColor="@color/color_primary_light"

ring-android/app/src/main/res/layout/frag_acc_jami_create.xml

@@ -49,6 +49,7 @@
             android:layout_height="wrap_content"
             android:layout_alignParentTop="true"
             android:layout_margin="@dimen/text_margin"
+            android:layout_centerHorizontal="true"
             android:textColor="@color/color_primary_light"
             android:gravity="center"
             android:text="@string/account_creation_ring"

ring-android/app/src/main/res/layout/frag_acc_jami_link.xml

@@ -20,6 +20,7 @@
             android:layout_height="wrap_content"
             android:layout_alignParentTop="true"
             android:layout_margin="@dimen/text_margin"
+            android:layout_centerHorizontal="true"
             android:textColor="@color/color_primary_light"
             android:gravity="center"
             android:text="@string/account_link_device"