Fallback values: use different gauge

[ajrobbins]

PWD has suggested that we use values from this gauge, which is on the Delaware River: https://waterdata.usgs.gov/nwis/uv?014670261 as fallback and during the down months for our primary gauge. I think we should still fall back to #17 in case the whole API is down, but in cases where our primary gauge is down, we should use the other gauge's values.

[ajrobbins]

When we fall back to using the Delaware River gauge, we should show this text: The Schuylkill River is the largest tributary of the Delaware River Watershed. This information is coming from a gauge on the Delaware River. We'll have to play with the styling on it, though.