Adds initial test support

Lil' first take on adding support for tests to `seed-element` based on `test-element`. To get this running, `bower install` then run a server and navigate to `tests/runner.html`.

Some topics we can talk about:

* Should we include some basic functionality that we can demonstrate being tested?
* If so is the current functionality sufficient?
* Should `tests/runner.html` be renamed to `index.html` so you can just navigate to `/tests` and have that run?
* Should any Karma config be included at this point?
* Any way we can get in support for a `test` button in our docs page?

cc @ebidel @robdodson