adding a clear button to elm

Clears all the logs that have been stored thus far.
![elmlogger8](https://cloud.githubusercontent.com/assets/2818455/5305043/d6300e46-7bac-11e4-9f5b-10e8c5e21dc6.png)

This should probably be a post because it is destructive. And then on the server after doing the post, do a redirect back to the main page. This is called the post-redirect-get pattern and is HTTP-friendly, as well as being user-friendly because the redirect to `get` means that the user can refresh the browser without the "do you want to re-post the data" dialog.