Add support for enable/disable inifinite scoll flag, fix jshint warnings

There's now a flag for enabling/disabling the
 infinite scroll -- it drives me nuts otherwise ;)

I've also created a generic `config` variable inside the `hn` object for future config options to use.

The extension still needs a config UI (instead of hardcoded settings in the source) and will likely need to store the `config` in localStorage.