GRADLE-1441: Add web facet and exploded web artifact to web projects

Enhancement for the IDEA plugin: Adds the web facet to the projects iml file and the corresponding exploded web artifact to the ipr file from the root project with all dependencies.

The implementation is partly based on the change made by Peter Niederwieser for the Scala configuration. I've extracted reusable code to an abstract base class and I've enabled the 'addsScalaFacetAndCompilerLibraries' test to ensure that the Scala configuration still works after my changes. He has disabled this test for being unstable. During my work I had no problems with this test at all and therefore I haven't disabled the test again.