Misc updates for the newest VM

BIOM is now forced to use `SparseMat` as a backend using a new configuration file.

To test and make sure that it is working for you, you can call the following lines in `www/handler.psp`:

```python
import logging
from biom.util import load_biom_config
logging.debug('BIOM %s' % load_biom_config()['python_code_sparse_backend'])
```

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Once this pull request is merged, I'll update the virtual machine.