work on 3D ROI structures
- wrote _reformat_masks to store mask as a list of lil_matrices
- im_shape is stored as a 3-tuple now
- mask property asserts that len(mask) == im_shape[0] and returns list of lil_matrices
Merge branch '3D_SIMA' of losonczy-server:/opt/git/sima into 3D_SIMA