Add constraints to all default models

[nreinicke]

Now that we have quick methods to do visualization from #21, we should start training our default model library with feature constraints. For example, when building out a model config it might look like this:

feature_set_1 = pt.FeatureSet(
    features=[
        pt.DataColumn(name="speed_mph", units="mph", constraints=pt.Constraints(lower=0, upper=120)),
        pt.DataColumn(name="grade_dec", units="decimal", constraints=pt.Constraints(lower=-0.2, upper=0.2)),
    ] 
)
feature_set_2 = pt.FeatureSet(
    features=[
        pt.DataColumn(name="speed_mph", units="mph", constraints=pt.Constraints(lower=0, upper=120)),
        pt.DataColumn(name="grade_dec", units="decimal", constraints=pt.Constraints(lower=-0.2, upper=0.2)),
        pt.DataColumn(name="road_class", units="category_0_to_5", constraints=pt.Constraints(lower=0, upper=5)),
    ] 
)
distance=pt.DataColumn(name="miles", units="miles")
target=pt.DataColumn(name="gallons_fastsim", units="gallons_gasoline")