Apply transform for custom axes order when mapping between channel space and CCF space

[kabilar]

The channel_locations.json stores the channel coordinates and origin. If the axes order can be configured in the IBL Ephys Atlas GUI, then this element will need to load the axes order and apply the transform when mapping between channel space and CCF space.

Along the same lines, need to determine why shifting by the origin is done differently for the x/z axes versus y axis (i.e. why subtraction versus addition).

# by adjusting xyz axes & offsetting from origin position
# in "pos_xyz_raw", x-axis and y-axis are swapped, correcting for that below
pos_xyz[:, 0] = pos_origin[1] - pos_xyz_raw[:, 1]
pos_xyz[:, 1] = pos_origin[0] + pos_xyz_raw[:, 0]
pos_xyz[:, 2] = pos_origin[2] - pos_xyz_raw[:, 2]

For further details, see discussion in pull request #3.