Compatibility with IRIS indexer

[d-chambers]

We should think about making WaveBank's public methods compatible with IRIS' indexer module in ObsPy. It would be nice if users could interact with either one in a seamless way.

[d-chambers]

I think this may be something to look at in the future as the indexer module is structured a bit different than WaveBank, eg the indexing and data access are different classes. Additionally, we should see if anyone requests this before we go adding more surface area to the API.