Themes: Redesign themes section

Add live previews for accents, icons shapes and more

Signed-off-by: AndroBuddy <anirudhchimpidi8@gmail.com>
Signed-off-by: Hưng Phan <phandinhhungvp2001@gmail.com>

res/drawable/accents_tiles_preview.xml

@@ -0,0 +1,27 @@
+<?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.
+-->
+
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item>
+        <shape android:shape="rectangle">
+            <size android:width="314.44dp"
+                android:height="125dp" />
+        </shape>
+    </item>
+    <item android:drawable="@drawable/tiles_shape_preview" android:gravity="right"/>
+    <item android:drawable="@drawable/accent_elements_preview" android:gravity="left"/>
+</layer-list>