feat(tooltipProvider): added appendToBody option for $tooltip

Okay, in re #139 I decided to just create a completely independent option called `appendToBody` for now. When `true`, the tooltips will be appended to the body. I do not think this is the best long-term solution, but until someone comes up with something brilliant for containers, this will do.

I intentionally did not update the docs. I think before we unleash the `$tooltipProvider` on the public, we should add a few more options to it, some proper defaults, and a few more detailed tests.

I also did not update the demo as that is not feasible in this case (needs a `config` block). But all the tests pass and I created a [working Plunker](http://plnkr.co/edit/OAtk4gUhqGx8R6ZeYH6T?p=preview).

This doesn't close #139 as that's still an issue, but it provides a good stopgap. 

What do y'all think?