[ENH] Include custom ODFs

[kellychang4]

Add argument for sh basis types. Force legacy basis types to FALSE.

Starting edit to incorporate custom ODF files into workflow. Need to separate ODF model estimation from tracking procedure.

[36000]

I wonder if odf_model should be renamed fodf_model and made its own task in tractography.py in the tasks folder. then it could be from an image file or a string, and that method in the tractography task folder either calls the appropriate data task method if its a string or calls the imagefile function if its an imagefile, similar to 'brain_mask'. this could also just be handled with if statements in the tractography method. I will work on this tomorrow

[kellychang4]

[...] made its own task in tractography.py in the tasks folder. then it could be from an image file or a string, [...]

I think if we go down this route to allow for custom fODF images that it would unlink these two procedures. I am in support of making them two separate tasks.

[arokem]

After a conversation with @36000, I think that maybe we remove the "legacy" and "basis_type" options here, and leave that up to the user. Then, this code would still allow users to provide custom ODFs, but they would have to make sure that the coefficients are for the "descoteaux" basis set, and they'd have to do their own conversion in advance for this. @kellychang4 : WDYT?

[kellychang4]

That is fine with me, so long as it is written somewhere!

[arokem]

For future reference (and maybe to be added to DIPY at some point?), we've discovered this function: https://github.com/scilus/scilpy/blob/master/scilpy/reconst/sh.py#L560, which can be helpful for users of this functionality.

[36000]

@arokem once these tests pass, this is ready to review/merge. kelly has signed off too