Add Tax Classes and tables

[johndcoy]

It doesn't appear to include tax classes or the tables for each.

[jessepearson]

When you say tax classes, do you mean the additional tax classes?

Image Link: https://d.pr/i/rXSECS

And the tables, are you referring to the rates for those?

I thought it was grabbing the classes themselves, but I purposely don't get the rates since it has its own csv export/import tool. Tax rates can also turn into several mb of data, so I didn't want to include them for performance reasons.

Just double checked the classes, and they aren't pulled through, so I will get to fixing that.

[jessepearson]

@johndcoy You mind testing out the PR?