Improve subglide highlight plotting function to autofind a good example

[ryanjdillon]

Not that important, but the current routine to demonstrate the found sub-glides requires passing the start/stop indices of the the data to visualize as automatically finding a good region would be really tricky.

Just in case I have too much time on my hands in the future.

smartmove/ann/figures.py/plot_sgl_highlight()

[ryanjdillon]

I found a decent section of data for the paper figure by looping over 1800 sample intervals, generating a plot for each` to compare.