updated and fixed bayes-itc

Cleaned up a few messy leftovers for data validation, made P6 peak
picking (for PLI window setup) automatic, set up the ES calculation,
and added comments.
Also reverted to one-sample t-test of differences since in the
reference data, PLI diffs work a LOT better than raw PLIs (possibly due
to the expected significant baseline differences that will get washed
out with a pooled baseline for proper diffs).