Themes: Add Live previews for applied themes and fonts

Co-authored-by: ender1324 <ender1324@abv.bg>
Signed-off-by: AndroBuddy <anirudhchimpidi8@gmail.com>
Signed-off-by: Hưng Phan <phandinhhungvp2001@gmail.com>

res/layout/base_preview.xml

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+    Copyright (C) 2020 ProjectFluid
+
+    Licensed under the Apache License, Version 2.0 (the "License");
+    you may not use this file except in compliance with the License.
+    You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+    Unless required by applicable law or agreed to in writing, software
+    distributed under the License is distributed on an "AS IS" BASIS,
+    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+    See the License for the specific language governing permissions and
+    limitations under the License.
+-->
+
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	xmlns:tools="http://schemas.android.com/tools"
+	android:layout_width="match_parent"
+	android:layout_height="180dp"
+	android:layout_gravity="center|top">
+
+    <ImageView
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:scaleType="centerCrop"
+        android:background="@drawable/preview_wallpaper"
+        android:src="@drawable/preview_base"
+        tools:ignore="ContentDescription"/>
+
+</LinearLayout>