Support NUnit test properties

[elv1s42]

Implements #87

[elv1s42]

@NikolayPianikov, I came back with a new pull request.

The tricky part was to send the properties from [TestFixture] and [TestCase] attributes. In both cases, the properties were saved inside <test-suite ... event, meaning we have to send the test metadata only when the test suite is finished (it means that all tests inside the suite are finished too, and the corresponding flows are closed). To send the test metadata after the test is finished, I need to send it with the .dll name, so now I have to collect a .dll name for each test as well as the test events inside each test suite to be able to send the service messages to TC when the test suite finishes.

Thank you!