FIX coreg_gui:  on initialization, ignore subjects_dir if it is not a directory
REV/DOC KIT head shapes:  drop support for pickled head shapes
TEST
TEST coreg:  fit_matched_points
ENH coreg:  make fit_ functions more similar

- add out='trans' option to fit_point_cloud
- RF:  transformation parameter to transformation matrix conversion
ENH kit2fiff:  automatically decimate head shape points for files with too many points
TEST coreg:  fit_point_cloud
ENH coreg_gui:  default MRI head shape color
STY in kit2fiff TEST
API:  expose more in mne.transforms
FIX/TEST kit2fiff:  transformation into MNE head coordinates
STY
ENH coreg_gui:  set busy cursor when fitting
ENH scale_labels():  option to include all labels
DOC:  coregistration manual
ENH gui:  show info dialogs in assert_env