Plot Confidence Intervals

[harper-wavra]

For the frequency plots we should also be plotting the confidence intervals.

"When we do add confidence intervals we need to probably force users to only select 1 curve so we don't get confused with too many plots. The confidence intervals are computed using the covariance matrices and the row vector data.
We can talk more later, but let's add an issue as a future enhancement to add CIs." - Pete