feat(testrunner): introduce environments

[dgozman]

Intended usecase is to have "class of tests" defined once, which can be used in any test suite.

const pageEnv = environment('page environment', () => {
  beforeAll(() => {});
  afterAll(() => {});
  beforeEach(() => {});
  afterEach(() => {});
});
testRunner.testAttribute('page', t => t.environment(pageEnv));
testRunner.pageIt = testRunner.it.page;  // optionally


// Later on:
describe('my suite', () => {
  it.page('test', () => {});
  pageIt('test', () => {});  // optionally
});