Upgrade to SLF4J 1.7.28, Groovy 2.5.8, RxJava 2.2.12, Joda-Time 2.10.4, Rome 1.12.2, OkHttp 3.14.3, Apache HttpClient 4.5.10, Apache Johnzon 1.1.13

Includes updated javadoc links for 5.1.x branch.

Includes Hibernate Validator 6.0.17 and renames "withoutJclOverSlf4j".

Includes Mockito 2.25, Undertow 2.0.19, OpenPDF 1.2.10, JRuby 9.2.6.

Includes RxJava 2.2.6, Netty 4.1.33, Undertow 2.0.17.

Includes OkHttp MockWebServer 3.12.1.

Includes JRuby 9.2.5 and Jetty Reactive HttpClient 1.0.2.

Includes Hibernate ORM 5.1.17 for integration tests.

Includes JAX-WS 2.3.1, Awaitility 3.1.3, OkHttp 3.12, Woodstox 5.2.

Issue: SPR-17446

Includes reordering of web dependency declarations.

Includes Hibernate ORM 5.1.16 and Hibernate Validator 6.0.13.

Also includes Apache Johnzon 1.1.9.

Includes XMLUnit 2.6.1 and Undertow 2.0.13.

Issue: SPR-16115

Includes upgrade to Hibernate ORM 5.3.5, EclipseLink 2.7.3, Selenium HtmlUnit Driver 2.32.1, Jetty 9.4.12 RC2.

Includes Groovy 2.5.2, Undertow 2.0.12, Hibernate Validator 6.0.12.

Issue: SPR-17129

Includes latest dependency updates (Mockito 2.21, Log4J 2.11.1, Hibernate ORM 5.3.4, Protobuf 3.6.1, JRuby 9.2, HtmlUnit 2.32, Selenium 3.14) for Spring Framework 5.1.

Issue: SPR-16388
Issue: SPR-16239

Issue: SPR-17058

Prior to this commit, the generated POMs for Spring Framework modules
would contain unneeded/harmful information from the Spring Framework
build:

1. The BOM imports applied to each module by the dependency
management plugin, for example for Netty or Reactor Netty.
Spring should not export that opinion to its POMs.

2. The exclusion of "org.slf4:jcl-over-slf4j" from *all* dependencies,
which made the POMs much larger than necessary and suggested to
developers that they should exclude it as well when using all those
listed dependencies. In fact, only Apache Tiles currently brings that
transitively.

This commit removes that information from the POMs.
The dependencyManagement Gradle plugin is disabled for POM generation
and we manually resolve the dependency versions during the generation
phase.
The Gradle build is streamlined to exclude "org.slf4:jcl-over-slf4j"
only when necessary.

Issue: SPR-16893

Issue: SPR-16470