Added external data support

[AndrewDessin]

I added in the ability to specify paths to both the model/trained data, and a path to find the current activity, or current X which we are trying to fit.

If a path is not specified, the normal flows continue.

[coveralls]

Coverage decreased (-2.5%) to 88.177% when pulling 6842ae4 on AndrewDessin:master into 30befb0 on kootenpv:master.

[kootenpv]

Great! It works fine :) Just wondering: shouldn't learn also have extra arguments?

[AndrewDessin]

Yeah, I was a bit indecisive about it. The reason I didn't include external Learn args is because learn takes one location at a time, collects the data for that location, saves it to files, and calls the train_model() method. Instead I created a new train argument.

I assume that the external user will already have collected their data by locations and stored them as files by location. Therefore, I really only need to train the model. So that is why I added a new train argument, instead of adding arguments to learn. Do you agree?

[kootenpv]

Yea, that makes a lot of sense. Again, thanks! Nice PR :)