pybids API is changing

[yarikoptic]

With bids 0.6.5+89.gb25be29 expect

    from bids.grabbids import BIDSLayout
ImportError: No module named grabbids

due to 0.7 changes bids-standard/pybids#247:

The module names are simplified: grabbids is now gone (in favor of layout) and bidslayout.py and bidsvalidator.py are just layout.py and validation.py. A deprecation warning is no longer issued (we had said this change would happen in 0.8, but I think it's better to introduce it early and have people fix all of the breaking changes at once).