Add JDK8 test
Add Jdk8 test to ApplicationSpec. To prevent https://github.com/codeborne/play-tests/issues/4
one needs to set "systemProperties['precompiled'] = 'false'" in play-tests' build.gradle.

And don't forget to set "sourceCompatibility = 1.8"
Workaround to include docviewer module to play-tests scope.
Prerequisites: "cd $PLAY_HOME && play build-module".