#261 upload country matrix with committees and assignments.

WARNING: This will sweep all countries, assignments and committees already created because its recreating them. Still need to write a unit test. And it probably doesn't need to sweep because of get_or_create
By changing the logic around, we can reduce the boilerplate a little bit:
```python
if not row[2] in committees:
    committees[row[2]] = Committee...
committee = committees[row[2]]
```
But even more than that, we could abstract the boilerplate of checking/updating the cache into its own function:
```python
def get_model(model, name, cache):
    if not name in cache:
        cache[name] = model.objects.get(name=name)
    return cache[name]

committee = get_model(row[2], Committee, committees)
```