Supporting code for running predict() on data other than training dat…

[jmarcusse]

…a with lgb

Non-training data can now be fed into the predict() function for the lgb_modeler using the argument custom_data.

This mirrors the process for the tensorflow modeler.

Steps for when custom_data is entered:

• Verify that all of the columns used in the trained model are included in custom_data
• Ensure that datetime models are converted to numerical in a manner consistent with the training data

[jmarcusse]

@agelder Let's discuss this change, which is a little complex and requires some judgment calls.