implement a __contains__ method in model/brain object

This is will allow to test for locations in model or brain object e.g.

```
loc = [34, -20, 50]
loc in bo # returns True if present
loc in mo # returns True if present
```

Inspect the model and brain object implementations to find where their stored locations are represented and how membership is currently queried. Add membership behavior matching the examples for both objects, then run the existing test suite and verify present and absent locations return the expected results.

Written by the indexing model from the issue text.