add a bffile datasource and bioformats load path in image.py

[barentine]

Addresses issue #bioformats installation. Posting as a draft for discussion - unclear if this is a direction we're interested in or not, but it was helpful for me to load some nd2 files from a collaborator.

Is this a bugfix or an enhancement?
enhancement
Proposed changes:

• add option to load using bffile

loading tested with

• single-channel nd2 file
• multi-channel nd2 file

untested
-time series

• other file types

[David-Baddeley]

Sounds good to me. Is installing bffile relatively painless? Is it painless enough that w might consider adding it to our dependencies?

[David-Baddeley]

I especially like the fact that it has a lazy loader (although the terminology is slightly misleading - asarray would usually imply forcing into memory ...)