Detach the HTML reporter

This is the first step needed to set the reporter interface.

There are still a lot of things to do, but I already want to share to allow earlier reviews, because it's necessarily huge.

It's still **WIP**, but **every** single commit is **passing** through the tests.

Btw, the last commit (@7de03f9) is passive of insane memory leak. (fix is coming) 
anotther copy/paste from `src/core.js`, it was the QUnit.load callback, ref: https://github.com/jquery/qunit/pull/603/files#diff-7eb52b366866677666470e019283c8eaL477

I agree 100% we can refactor this, but I prefer to address this one in a new issue/PR, for now it's just detaching.