Upgrade to Thymeleaf 3 and drop support for Thymleaf 2

This commit raises the minimum supported version of Thymeleaf to
3.0.x. It also upgrades Spring Social to a version that is compatible
with Thymeleaf 3.

Closes spring-projectsgh-7450
Closes spring-projectsgh-6258
See spring-projectsgh-7885

Author: wilkinsona

spring-boot-autoconfigure/pom.xml

@@ -526,6 +526,11 @@
 			<artifactId>spring-social-web</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework.social</groupId>
+			<artifactId>spring-social-web-thymeleaf3</artifactId>
+			<optional>true</optional>
+		</dependency>
 		<dependency>
 			<groupId>org.springframework.social</groupId>
 			<artifactId>spring-social-facebook</artifactId>
@@ -553,7 +558,7 @@
 		</dependency>
 		<dependency>
 			<groupId>org.thymeleaf</groupId>
-			<artifactId>thymeleaf-spring4</artifactId>
+			<artifactId>thymeleaf-spring5</artifactId>
 			<optional>true</optional>
 		</dependency>
 		<dependency>
@@ -571,11 +576,6 @@
 			<artifactId>thymeleaf-extras-data-attribute</artifactId>
 			<optional>true</optional>
 		</dependency>
-		<dependency>
-			<groupId>org.thymeleaf.extras</groupId>
-			<artifactId>thymeleaf-extras-conditionalcomments</artifactId>
-			<optional>true</optional>
-		</dependency>
 		<dependency>
 			<groupId>org.thymeleaf.extras</groupId>
 			<artifactId>thymeleaf-extras-java8time</artifactId>

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mobile/DeviceDelegatingViewResolverAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2016 the original author or authors.
+ * Copyright 2012-2017 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,7 +16,7 @@
 
 package org.springframework.boot.autoconfigure.mobile;
 
-import org.thymeleaf.spring4.view.ThymeleafViewResolver;
+import org.thymeleaf.spring5.view.ThymeleafViewResolver;
 
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/social/SocialWebAutoConfiguration.java

@@ -18,7 +18,7 @@
 
 import java.util.List;
 
-import org.thymeleaf.spring4.SpringTemplateEngine;
+import org.thymeleaf.spring5.SpringTemplateEngine;
 
 import org.springframework.beans.factory.ObjectProvider;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;