raws_leaflet() function

[jonathancallahan]

We should be able to handle all raws stations in a single leaflet map.

This function will take the metadata dataframe as input and create a leaflet map where users can select their station of interest and see the relevant metadata in a popup. It will be very similar to:

https://github.com/MazamaScience/AirSensor/blob/master/R/pas_leaflet.R