Add weather warnings

[dhouck]

I don’t know if either of the current backends support NWS alerts or their non-US equivalents. I don’t see any indication of it from a brief look at the site, but I could have missed something.

On the front end this could just display as a little yellow or red exclamation point before the description of the weather (so it might say ! Heavy snow instead of just Heavy snow), perhaps with the color dependent on the severity of the alert.

[schachmat]

This should be added when we have a backend service supporting it. I'll leave this issue open for tracking progress.

[Silent-Hunter]

Maybe it would also be good to have a link to the full text of the current warning, or some other way of displaying the full text, as well. If it's possible to support that.