[IMP] theme_bookstore: update the theme

This commit updates the theme to improve the design with new colors, new
pictures and new snippet customizations.

task-2557935

Part-of: odoo/design-themes#500

theme_bookstore/views/snippets/s_quotes_carousel.xml

@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="utf-8"?>
+<odoo>
+
+<template id="s_quotes_carousel" inherit_id="website.s_quotes_carousel">
+    <!-- Carousel item #1 -->
+    <xpath expr="//div[hasclass('carousel-item')]" position="attributes">
+        <attribute name="style">background-image: url('/web/image/website.s_quotes_carousel_demo_image_6'); background-position: 50% 50%;</attribute>
+    </xpath>
+</template>
+
+</odoo>