Add support for NUnit's SetUpFixtures

Currently, SetUpFixtures are not included into the report. Ideally, they should be collected automatically, with no additional efforts, so the following code:

```csharp
using NUnit.Framework;
using NUnit.Allure.Core;

[SetUpFixture]
public class MyFixture
{
[OneTimeSetUp]
public void SetUp(){}

[OneTimeTearDown]
public void TearDown(){}
}

public class TestClass
{
[Test]
public void TestMethod(){}
}
```

should produce the following report:


#### Motivation
Same as #360: fixtures should be supported out-of-box.

#### Other information

Again, as for #360:

1. There should be a way to preclude a fixture from getting in the report for those who are used to the current opt-in approach to fixtures.
2. There should be a way to assign a custom name to a fixture (on a class or method levels).

Start by reviewing the NUnit SetUpFixture example in this issue and inspect the existing fixture-reporting behavior. Compare the requested automatic collection, opt-out behavior, and custom naming with merged pull request #380; done means SetUpFixture setup and teardown appear in the report without extra test-code changes.

Written by the indexing model from the issue text.