Improve efficiency of single-object queries

We frequently make use of the following general pattern:

```python
try:
    x = Asdf.objects.get(name='foobie bletch')
except ObjectDoesNotExist:
    handle_it()
```

This pull request slightly improves efficiency and (in my opinion) readability by changing that code to the following:

```python
x = get_or_none(Asdf.objects, name='foobie bletch')
if not x:
    handle_it()
```

---
- [x] Migration works
- [x] Tests pass