This patch:
- makes environment a simple class with optional methods `beforeEach`, `afterEach`, `beforeAll`, `afterAll`, `globalSetup` and `globalTeardown`
- removes capability to have multiple hooks of the same name inside suite
- removes default environment for test. (`dit` now adds a `TraceTestEnvironment` to the test)
- extracts all environments that we use in our tests in `//test/environments.js`
Downsides:
- we no longer know hook locations for the environments. This, however, should not be a big deal since stack traces (if any) will still point into it.
- this also regresses hook locations for suites for simplicity. We can get them back, but it shouldn't be pressing since we now have only one hook of each kind in every suite.
