Working on plot_11

plot_11 now graphs 4 different type of graphs
- regular average upload and download, with all 4 carriers on the same
plot
- average upload/download of 4 carriers, differentiated by how average
was calculated (sliced mean vs real mean)
- LTE vs Non-LTE
- mobile vs netbook

Also added function to data_utils that finds the sliced mean, given a
number of standard deviations from the mean that you want to slice