Add spring-boot-versions project

Add a new maven project containing a versions.properties file and
an effective POM. Rework existing projects to use the versions
artifacts.

Partially reverts 307fbba9e4b88ea9938817a64d840d82d6a8cd72

Fixes gh-913
Fix broken relative path
Remove reference to resolved issues in Groovy
Add @IntegrationTest properties to Environment after system props

Fixes gh-910
Fix broken dependencies appendix
Upgrade to Spring 4.0.5

Closes #891
Merge branch '1.0.x'
Upgrade to Spring HATEOAS 0.12.0.RELEASE

Closes #801
Upgrade to RELEASE version of Spring Data Dijkstra release train

Closes #815
Combine maven-dependency-plugin declarations

Fixes #917
Correct the path used to import the dependency versions .adoc file
Only use the system classloader for Java agent classes

The JVM will always load Java agent classes using the System
classloader. Previously, LaunchedURLClassLoader would only use
standard class loading as a last resort which could result in a
Java agent class being loaded multiple times. This caused a problem
with Spring's InstrumentationSavingAgent as the second (and
subsequent) copy of the class would return null from
getInstrumentation() even though instrumentation was enabled.

This commit updates LaunchedURLClassLoader to always use standard
class loading for any classes in jar files referenced via -javaagent.
This ensures that such classes are only loaded once.