Improve error plots

[shorowit]

Suggested improvements:

1. Add horizontal lines that reflect the acceptance criteria (e.g., 5%, 500 kWh, 5 MBtu), so you can quick compare the results.
2. Use the same colors in both the absolute and bias plots. See below where orange is electricity_baseload in one plot and electricity_cooling in the other.
3. Exclude the second y-axis in the absolute error plot if the home has no fossil fuels (as below).

Example plots: