Add environmental plots

[Aariq]

Will close #21

Adds plots for:

• [x] ET₀
• [x] Plant available water
• [x] Comfortability index

[Aariq]

We're getting closer to finishing the "environmental" plots for the dashboard. This PR version currently looks like this:

The adjusted temperature plot shows arrows from the "true" temperature to the wind chill or heat index. Plant available water is currently faceted by basin and depth, and summarized to get the mean of the two sensors at each site, depth, and basin/non-basin.

A couple of questions:

• What are the units for plant available water?
• Is the faceting for PAW helpful? Alternatively I could average over basin/non-basin and just facet by depth, average over depth and just facet by basin/non-basin, represent basin/non-basin with linetype like we did in the soil tab, etc. Lots of options here to emphasize different comparisons.
• Do we still want to call this tab "Environmental"? (not that I can think of a better title)

Ideas/to-dos for me:

• I'm thinking of adding an "info" icon with a tooltip to each plot explaining them and including sources for equations
• Alternatively, there could be a single popover for the entire page triggered by an info button or link in the sidebar.
• Display a "no data available" message when dates are selected before ET0 measurements were recorded.

[Aariq]

Added card headers with popovers. Added a "no data available" message to the ET0 plot when dates before data collection are selected. Adjusted spacing and padding to make a bit more room for plots.

This is now ready for review