Replacing instance variable with private method
Adding spec for testing rendering override

I want to be able to expose a way for people to render custom views
for a given object. Conceptually we render `entities/show.html.erb`
for all work entity objects. But I want to allow type 'article' to
render some semblance of `articles/show.html.erb`.

It may mean we have:

```views
articles/hydramata/work/entities/show.html.erb
hydramata/work/entities/show.html.erb
```
Marking entity_render_spec as fast running
Adding spec for PropertySet#each