Includes latest dependency updates (Tomcat 8.5.20, Protobuf 3.4, RxJava 2.1.3, Caffeine 2.5.5)

Issue: SPR-15870

Issue: SPR-15814

This commit also fixes compilation with JDK9 since
KT-18832 has been fixed.

Issue: SPR-15814

Includes latest dependency updates (Hibernate Validator 6.0.1, Caffeine 2.5.4, Netty 4.1.14, Tomcat 8.5.19, Johnzon 1.1.2, JsonPath 2.4, Jython 2.7.1)

Issue: SPR-15839
Issue: SPR-15808

Sync 3.1.0.BUILD-SNAPSHOT changes to Operators.checkRequest (removed)

Issue: SPR-15737

Issue: SPR-15548
Closes gh-1488

Issue: SPR-15814

This commit updates BeanUtils class in order to add Kotlin optional
parameters with default values support to the immutable data classes
support introduced by SPR-15199.

Issue: SPR-15673

Issue: SPR-15791

Issue: SPR-15787

This binary format more efficient than JSON should be useful for server
to server communication, for example in micro-services use cases.

Issue: SPR-15424

Issue: SPR-15757

This commit introduces integration tests which verify that the
SpringExtension can be used in conjunction with JUnit Jupiter's
@ParameterizedTest support.

Issue: SPR-15733

Issue: SPR-15728

Issue: SPR-15686

Explicit typing for older jvm compilation in BodyExtractor

This commit introduces the Jackson2Tokenizer as a replacement for the
JsonObjectDecoder. The latter was dropped because of its complexity, and
hard dependency on Netty's ByteBuf.

The new Jackson2Tokenizer leverages the new non-blocking JSON parser,
using it to parse the incoming data buffers into TokenBuffers, each
token buffer representing one JSON object. As with JsonObjectDecoder,
it also supports streaming individual JSON array elements.

Issue: SPR-14528

Includes upgrade to Objenesis 2.6, Gradle 3.5.1, RxJava 2.1.1, JSON Binding API 1.0 final.

Issue: SPR-15686
Issue: SPR-15600

This commit also enables Kotlin build with JDK 9 since this new
version supports it.

Kotlin does not yet work with JDK 9, so we need to disable the Kotlin
plugin if we are using JDK 9.

Includes latest dependency updates (Commons FileUpload 1.3.3, OkHttp 3.8.1, XStream 1.4.10)

Issue: SPR-15407

Issue: SPR-15548

Changelog: https://github.com/JetBrains/kotlin/releases/tag/v1.1.2-5

Issue: SPR-15622

Issue: SPR-15590

Latest dependency updates (EclipseLink 2.6.5 RC2, JSON-B 1.0 RC2, Gson 2.8.1, Jetty 9.4.6, Netty 4.1.12)

Issue: SPR-15646

Avoid importing Kotlin 1.0.x from Mockito Kotlin and only depends on
kotlin-stdlib instead of kotlin-stdlib-jre8 since we don't use
additional jre7 or jre8 API.

This commit also removes extensions hidden by Java API (varargs).