FIX: Update and sync DTI episode

[kaitj]

This notebook clears the outputs of the DTI solutions notebook. It also fixes the links to static images within both solutions and non-sollutions notebook.

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[jhlegarreta]

On a slightly related note:

• The raw Jupyter notebook still works on the old dataset/subject:
  https://github.com/carpentries-incubator/SDC-BIDS-dMRI/pull/116/files#diff-f39308c39e30eb935f09d84c0059871a0559066723a7229280dba5dbc9d524e6R75

  https://github.com/carpentries-incubator/SDC-BIDS-dMRI/pull/116/files#diff-f39308c39e30eb935f09d84c0059871a0559066723a7229280dba5dbc9d524e6R77

  As with solutions notebook, the subject id should be defined at a single place

• The notebook fails when looking for the T1 even when updating to the new dataset/subject.

• The markdown and the Jupyter notebooks are still different when trying to look for the data.

Definitely they need to be synchronized (paying attention to the relative folder level when trying to look for the data).

[kaitj]

I have updating all of the jupyter notebooks (aside from the intro at the moment) on my to do list - waiting to finalize all of the exercises before doing so!

[kaitj]

A few updates since last review! Started with this one as it was the easiest of the 3 notebooks I'm working on updating.

1. Branch has been rebased from master.
2. Tried to fix (as best as I could) the characters per line in the markdown file
3. Synced markdown to both notebooks and updated the paths as needed - hopefully I didn't miss anything here.
4. Cleared output and remove solutions from non-solutions notebook.
5. Ran autopep8 over the jupyter notebooks, so should be pep8 compliant for the code cells.

It should be grabbing the subject at the beginning of the notebook (exercise not withstanding), let me know if I missed a cell!

[jhlegarreta]

Have not tried locally.

An inline comment. Otherwise looks good at first sight.

[kaitj]

Related to #100 - takes care of the DTI notebooks portion