Multi-OWL joins: Minor optimizations

[joeflack4]

Overview

The main method of creating a single OWL of all of OMOP is to split by vocab, create individual files, and then concatenate them together.

The only suboptimal thing right now is that annotation properties and classes are not grouped together. The first file has a group of annotation props, then classes, as does the second file when it gets concatenated, and so on.