Add unit tests

[thomasdigby]

These will be required at some point, especially when we need to merge pull requests etc.

CasperJS could be useful, Hugo uses it on his accessible Modal

• https://github.com/edenspiekermann/accessible-modal-dialog/blob/master/tests/index.js
• http://docs.casperjs.org/en/latest/testing.html

[thomasdigby]

Currently underway with Mocha/Chai. We need to scope out the necessary tests for all components and unique tests per component, also whether we incorporate cross-browser testing? It seems like we should be able to do this, we need to make sure the test suite supports the browsers we need to support. We can automate with phantomjs as well, but I'm not sure the benefit outweighs the pain in setting it up.

[thomasdigby]

Branch open: https://github.com/frend/frend.co/tree/feature/domtests