Update all ES queries to use Elasticsearch DSL (bug 1036168)

No, it ends up with a funky query. The kwargs apply to a single filter. I believe this is so you can do things like `qs.filter('term', field=value, boost=5, otherthing=something)` and they are all part of a single filter.

E.g.:
```
>>> WebappIndexer.search().filter('term', **{'app_type': 1, 'status': 4, 'uses_flash': False}).to_dict()
{'query': {'filtered': {'filter': {'term': {'app_type': 1,
                                            'status': 4,
                                            'uses_flash': False}},
                        'query': {'match_all': {}}}}}
```
isn't the query we're expecting with a bool filter:
```
{'query': {'filtered': {'filter': {'bool': {'must': [{'term': {'app_type': 1}},
                                                     {'term': {'status': 4}},
                                                     {'term': {'uses_flash': False}}]}},
                        'query': {'match_all': {}}}}}
```