Enh/afni4d (cleaned PR)

4d afni support: cleaned PR 
see: https://github.com/NeuroVault/NeuroVault/pull/36

Yeah, I had accidentally merged into my master and that made the diff wrong, I rebased off your merged master and that sorted it.  Yay git magic.

```
git fetch neurovault master
git rebase neurovault/master
git push -f origin master
```

G