Adding most commonly used parts of window.console. Fixes Issue#506. r=Ms2ger
auto merge of #1666 : ozten/servo/issue-506-add-basic-console, r=Ms2ger

Here is an attempt to fix Issue#506.

I couldn't figure out how to do variadic arguments to `console.log`, but I did test calling `console.log('foo', 'bar', 'baz')` and it prints the first argument and doesn't error out, which is nice.

window.console is not a web standards. I did the popular functions, but not some of the newer ones documented [on MDN](https://developer.mozilla.org/en-US/docs/Web/API/console).

This PR will allow more pages to load properly, where developers have left in window.console calls.