ENH: i/o for fiducials fiff files
ENH: option to raise an error when get_subjects_dir() finds nothing
ENH: add MriHeadFitter
ENH geom: import mayavi locally
cleanup/DOC

 - kw T => trans
 - geom only keeps one trans
ENH: add MriHeadCoreg Traits GUI
ENH: MriHeadFitter

 - assembe list of files to copy on __init__
 - look for source spaces with different iso parameters
STY:  cleanup method order
ENH: MriHeadCoreg gui

 - If target files exist, ask whether to overwrite
 - remove save-trans button
RF: use numpy array instead of matrix
ENH: traits gui
ENH: add FixDigHeadShape mayavi-gui
ENH: add FindDigPoint mayavi gui
RF: extract `find_mri_paths()` function
ENH coreg_gui: add HeadMriFitter
ENH: import shortcuts / mne.gui module
DOC
ENH: mri fitting with scaling

 - Make `MriHeadFitter` a subclass of `HeadMriFitter`
 - update giu
ENH geom: wireframe plotting (line_width=1 and lighting=False)
FIX coreg: MriHeadFitter