RequireThis rule and fixThis Gradle task

* `gradlew clean check -x test --parallel --continue` - to collect reports
* `gradlew fixThis --parallel` - to fix all possible vulnerabilities. With `-Dfile.encoding=UTF-8` on Windows

Since the `RequireThisCheck` doesn't see parents for anonymous classes (e.g. `Runnable` callback), its report doesn't contains the outer class name with `this.`,
therefore we still have to fix those cases manually.
Thanks to the wrong `replacer` just with `this.` we have uncompilable code enough easy to find problems.
Not so easy to fix for good readability though...

* Upgrade to Grade 2.12
* Upgrade to SonarQube native plugin

The fix contains at about 300 files. So, will be done on merge.

Fix `fixThis.gradle` according PR comments

Apply `fixThis` and also `fixModifiers` for test classes.
 Fix some `this.` inner issues manually.
 Make code polishing for long lines after `fixThis`

Fix conflicts and vulnerabilities after the rebase

spring-integration-mail/src/test/java/org/springframework/integration/mail/ImapMailReceiverTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2015 the original author or authors.
+ * Copyright 2002-2016 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.
@@ -893,7 +893,7 @@ public class ImapMailReceiverTests {
 
 			private boolean firstDone;
 
-			public TestReceiver() {
+			TestReceiver() {
 				setSearchTermStrategy(searchTermStrategy);
 			}
 

spring-integration-mail/src/test/java/org/springframework/integration/mail/config/MessageWithContentTypeTests.java

@@ -94,7 +94,7 @@ public class MessageWithContentTypeTests {
 	}
 
 	private static class TestMimeMessage extends MimeMessage{
-		public TestMimeMessage() {
+		TestMimeMessage() {
 			super(Session.getDefaultInstance(new Properties()));
 		}
 	}