Easy JUnit support

[UnknownJoe796]

This one shouldn't be too hard, though it will be harder than issue #5.

You will probably need the following to work on this:

• Some experience with working around build systems
• Some experience with using JUnit
• A willingness to research or knowledge of how to run JUnit manually
• Some willingness to get familiar with the principles of KBuild, especially how it models code modules. Shouldn't take too long, you'll likely need to review most of the publicly exposed interfaces.

We need JUnit support.

My recommended path is this:

• Create a JUnitModule interface
  • It should require a HasJvmJars module as a value
  • It should require a source root for the tests with a reasonable default
  • It should have a function called test(), which runs all of the tests
  • It should have a function called test(classOrTestName: String), which runs a subset of tests
  • Those functions should throw if the test fails
  • JUnit should be set up to output reports to a folder

Goals:

• The end-user should be able to add dependencies just for testing with ease
• The module should not be used to extend the end users' main module because IntelliJ views them as separate modules. Making it a separate module will ease IntelliJ support.