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)

You can actually just put a `name` attribute on the button and then the name/value pair will get posted. So you shouldn't need an extra hidden input.