This commit configures Checkstyle and updates the build to comply with
that configuration. The Eclipse JDT metadata has also been updated
so that the output of Eclipse’s code formatting and clean-up is
compliant with Checkstyle.
The use of the latest version (6.10.1) of Checkstyle has required an
upgrade to Gradle 2.7. Gradle hardcode’s the name of the Checkstyle’s
main class which has changed between version 5 (Gradle’s default) and
version 6.
Closes gh-119
