Add Legend for Hazard Overlay

We currently don't have any legend information for any of the overlays. I would argue that faults and plates are pretty self explanatory. I am not sure that adding them to the legend would offer our user's much valuable information. However, It would be nice to include a legend for the hazard information.

We could make the overlay legend information dynamic, but let's start by just adding it to the legend so that it is always visible.