keep bti_info as private attribute
add prop bti labels
favor attr over prop
dont be greedy
Merge pull request #1361 from maedoc/conserve-4d-ch-names

keep 4D ch_name in separate field
fix for pandas 0.15
Make fit_sphere_to_headshape work in more cases

 - Add flag to select which digitization points to use in
   `fit_sphere_to_headshape`.
 - Make `make_eeg_layout` still work even if no digitization points
   are present. Generate a warning though.
Tweak error message
Added tests, kinds now as tuple
Don't display warning during tests
Make user specify origin_head
Merged 3D to 2D mapping of electrode positions

There was a duplication of code for mapping 3D electrode positions
to a 2D space. Both the `_auto_topomap_coords` and
`make_eeg_layout` functions had their own implementation.
updated docstrings
Implement option 2

Raise warning when no digitization points are present
and no origin_head is specified.

Add origin_head parameter to topomaps.
Add separate testcase for _auto_topomap_coords