File Input Update [WIP]

[TomMaullin]

This PR includes a major rehaul to allow BLMM to accept any form of file input.

At time of writing, the rehaul is essentially complete and tested (none of the code requires explicitly NIFTI format but instead works with generic .dat files, only reading and writing datatype specific information at the beginning and end of the code). The only remaining issue is to allow for CIFTI and/or GIFTI inputs at the beginning and end of the computational pipeline.

[TomMaullin]

Update nib.load automatically handles reading in CIFTI files. However, blmm_cleanup must convert the images back to nifti/cifti format still.