added new frequency plots and code

1) Changed code to average a spectrogram over 20 seconds in the hamming
window.  Also interpolated all signals to the same sampling rate and
clipped out the sections that were not under the influence of
longitudinal perturbations
2) Changed "dusty purple" to "red" in each code and updated legend
3) Edited the text in the report to reflect the results in the new
graphs
4) Fonts are still strange when saving to pdf
I think these plots might technically be called "mean periodograms".