WIP Add slimerjs

Hi There,

I just wanted to get this up there to see what you guys thought. This is currently a work in progress to add [slimerjs](http://slimerjs.org/) to teaspoon.

###What I want to accomplish
- [ ] Support Slimjs
  - [ ] Standalone
  - [ ] Lightweight
- [ ] Add support for running multiple drivers in the same testing instance in the same CI

Not sure if this last one should be in this PR or another one, like I said I'm up for critique.