More tests needed for meshes with a broader range of element orientations

This issue was discovered in PR #53

Our tests at the moment only cover simple meshes with element-neighbor orientations that have a flip of 0. This is leaving out some conditionals in the `SideExchange` calls that are left unverified. We ought to identify some test cases that use meshes that help us touch on other element-neighbor orientations.

**Anyone who wants to tackle this will be given a free account on [Fluid Numerics Galapagos cluster](https://galapagos.fluidnumerics.com/).**