check dipy compatibility

[matteofrigo]

With the recent update of dipy, many functions will not work.
There are two possible solutions:

• Require an old version of dipy (suboptimal)
• Do a complete revision of the parts of dmipy where dipy is used (will take longer than expected)

What do we do @rutgerfick ?

[rutgerfick]

Where are the spots you think it's broken? only median_otsu?

The python3 tests pass with dipy 1.0, so it must be something that's not in the tests.

[matteofrigo]

For sure median_otsu, but I think it will be better to go through the whole list of changed functions and just check if they are used anywhere. Although it's mostly streamlines-related functions, which makes the job much easier as they are never used in dmipy.

For the records, one case in which median_otsu is used is discussed in #76 .