Simplify StackWidgetService; reduce flicker

uhabits-android/src/main/res/layout/widget_empty.xml

@@ -0,0 +1,50 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  ~ Copyright (C) 2016 Álinson Santos Xavier <isoron@gmail.com>
+  ~
+  ~ This file is part of Loop Habit Tracker.
+  ~
+  ~ Loop Habit Tracker is free software: you can redistribute it and/or modify
+  ~ it under the terms of the GNU General Public License as published by the
+  ~ Free Software Foundation, either version 3 of the License, or (at your
+  ~ option) any later version.
+  ~
+  ~ Loop Habit Tracker is distributed in the hope that it will be useful, but
+  ~ WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+  ~ or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+  ~ more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License along
+  ~ with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<FrameLayout
+    xmlns:tools="http://schemas.android.com/tools"
+    android:id="@+id/frame"
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:gravity="center"
+    android:orientation="vertical">
+
+    <LinearLayout
+        android:id="@+id/innerFrame"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:orientation="vertical"
+        android:paddingTop="4dp"
+        android:paddingLeft="8dp"
+        android:paddingRight="8dp"
+        android:paddingBottom="4dp"
+        tools:ignore="UselessParent">
+
+        <TextView
+            android:id="@+id/title"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:gravity="center"
+            android:textColor="@color/white"/>
+
+    </LinearLayout>
+
+</FrameLayout>