feat(core): include scenario object in engine hooks

[bernardobridge]

Why

Addresses #932

It's useful for test authors to have access to the current scenario being ran for multiple reasons, one of them being the use case explained in that issue.

Given the following function:

function myBeforeScenarioHandler(context, ee, next) {
    console.log(context.scenario)
    next();
};

All of the chosen scenario is available in context.scenario.

---

Note: removed unrelated index.js from tests that was no longer being used after test change in another PR.

[bernardobridge]

compile function was being passed scenarioSpec.flow but not doing anything with it, therefore the change here doesn't really impact anything, and we can now use the whole object.