Moved TestReporter helper type to Helpers file
Changed TestRunnerSpecs to new matcher

Allows them to be merged with selftests.fs
Merged Selftests.fs and TestRunnerSpecs.fs

The Selftests were to begin with full-stack tests. Now, after test reporting
has been abstracted, the self tests have been rewritten to verify the test
runner behaviour, and have therefore been merged with test runner specs.
Cleanup disposables in test context
Shared common setup as common subject