Optionally accept featuretools feature objects in generate_pipeline_example

[jeremyliweishih]

Currently in generate_pipeline_example we receive a features_path, read in the features from such path and then use the same path in the pipeline example. However, what if the user wanted to specify a different path in the example itself? This issue tracks optionally accepting the features objects directly to load the the features to use in generate_pipeline_example.