Align layer/legend titles, content, ordering

[brucecrevensten]

Feedback:

It might be more clear if the headers on the legends matched the name of the layers in the clickable list (right now the info ro the "air quality forecast" is labeled "projected air quality index" and "air quality sensor network" is labeled "air quality sensors").
Also, when both air quality layers are clicked on, the information about the sensor network is below the info about the forecasts, but that's not the order they're listed in the clickable layers. Can the sensor info go above the projected AQI when both are clicked on? Would it be possible to make the PurpleAir legend match the Projected AQI legend so that it has the good/moderate/unhealthy text? And maybe also add the sentence from the projected air quality information "this layer shows AQI" to the information that goes with the PurpleAir legend? It would be good for each layer's information to stand alone in case people only have one layer clicked on. Can we also add a sentence to send people here for more information on PM2.5?

[brucecrevensten]

• [x] Legends match titles
• [x] Fix order of legends to match layer order
• [x] Use same legend table for PurpleAir and Air Quality Forecast layers
• [x] Mirror language between PurpleAir / Air Quality Forecast layers
• [x] Add link to EPA PM site