Add warning to Problems view when a test fails #14

As an alternative to keeping the JUnit view open all the time, it would be handy to have notification of test failures show as warnings in the Problems view.

Ideally, the location of the warning (i.e. where you jump to you when you click the warning) should be the top of the stack trace from the test failure. And the description text of the warning should be the exception/error message (e.g. "AssertionError: expected: but was:"). The type of the warning can be something like "Test Failure" for fails and "Test Error" for uncaught throwables.