ENH: Extended MRtrix3 interface

[matteomancini]

Changes proposed in this pull request:

• Added interfaces to mrconvert, dwiextract and mrmath (for operations on single images) not previously included in the mrtrix3 interfaces;
• Updated interfaces to 5ttgen, dwi2response and dwi2fod taking into account the new syntax in the latest releases of MRtrix3 and offering the chance to use multi-tissue constrained spherical deconvolution.

[matteomancini]

I see again some conflicts (not present before) that I am not able to resolve. Do I need to merge master again?

[satra]

@matteomancini - yes - my worry with the previous set of changes is that it seemed to revert changes in master. so one option is to merge with master, resolve any conflicts and then push here. if the changes look fine great. if they look like they are reverting some intended changes (such as adding spaces, where there shouldn't be), then close and start another PR.

[effigies]

This looks like one of those weird GitHub issues. Running a diff from this branch to master on the command line is much more reasonable.

I'm closing this PR. @matteomancini can you open a new PR on the same branch? It should have a much simpler diff.

[matteomancini]

The issue was committing the changes without the last check-before-commit, the last commit ("fixed tests") was correct. In any case, I opened a new PR: #2338