Add maximum error picket and leaf to results_data

[bearner-hca]

In version 3.0, it would be useful if the max_error_picket and max_error_leaf of the picket fence module were accessible through results_data.

Currently I access these values directly from:

pf = pylinac.PicketFence(BIN_FILE.path)
pf.analyze(tolerance=tolerance, action_tolerance=action_tolerance)
pf.max_error_picket
pf.max_error_leaf

But this is inconsistent with the way other data is accessed in Pylinac.

I would prefer:

pf = pylinac.PicketFence(BIN_FILE.path)
pf.analyze(tolerance=tolerance, action_tolerance=action_tolerance)
data = pf.results_data()
data.max_error_picket
data.max_error_leaf