Support "is it daylight" as a valid data point for safety matrix thresholds

[MoralCode]

https://github.com/RIT-Rowing/RiverStatusBoard/blob/470165884b0a339804d078cfc41e3648c054db4c/scripts/safety-matrix.js#L76-L81

[MoralCode]

All that would be needed for this is support for computing datapoints based on others (i.e. take sunrise and sunset time and the current time (possibly with some model of the different phases of sunrise/twilight) and compute whether its likely to be daylight outside

[MoralCode]

TRRA could use this for theirs - zone 5 has an IF DAYLIGHT condition