plot_weather.py should automatically select y-axis limits

[jamessynge]

The annual temperature range in Massachusetts (home of PAN006) is fairly large, especially when you include both ground and sky temps. For ambient, the range in the last 6 months has been about 100F. This is vastly different than the situation experienced by PAN001, which has a much lower annual range.

plot_weather.py uses limits in peas.yaml, such as:

    plot:
        amb_temp_limits: [-5, 35]
        cloudiness_limits: [-45, 5]
        wind_limits: [0, 75]
        rain_limits: [700, 3200]
        pwm_limits: [-5, 105]

I propose that these limits be auto computed from some time range (e.g. just the data in the daily plot, or the last week, etc.).

[wtgee]

The only worry with it being constantly re-computed would be that they would look inconsistent when just glancing from plot to plot, which could be annoying and/or misleading. The previous week would probably mitigate that.

The plot was all built by @joshwalawender, who may or may not have some advice on this.

More could change with this as well, e.g. for those of us who don't have an anemometer it would be nice to just not show the wind.