Nifti read

This implements most of what we talked about in this discussion: 

https://github.com/vistalab/vistasoft/pull/73

Please take a careful look, because this touches many files, all over the code-base. We should be careful merging this! Also, I have not come to a conclusion about writeFileNifti. @frakkopesto: it seems that you have edited the .m file to be compatible with what the mex file is doing - is this important to preserve, with niftiWrite refactored, or should we get rid of writeFileNifti (both the mex/c code and the .m version)?