Pre-Alpha-MVP: HTML5/laptop-microphone solution

Having had a few discussions around what range of frequencies we want to be able to capture and why (see #7), it's become clear that we really need to start with a simple solution, get the results from that and only _then_ figure out what the best 'next steps' might be; i.e. the _agile approach!!_

So as @nelsonic mentioned in #7:

> As a "Pre-Alpha-MVP" it might be an idea to do this using HTML5 and the Microphone on a Cheap 2nd Hand Chromebook instead of a RaspberryPi/Arduino ...
@jasonpecor appears to have attempted this: https://github.com/jasonpecor/DecibelMeter so we might be able to get some pointers from his work... however jasonpecor/DecibelMeter#6 so... might need some work...

The repo is great as a starting point, and I think could perhaps be improved by having a quick google of the HTML5 Audio API and summarise what it can/can't do, and see how we can use that with the default microphone in our laptop.