FIX: Set L/R labels in orthoview correctly

[effigies]

Orthoview displays in neurological convention (left on the left, etc.) but places labels as if the display is radiological. This fix simply changes the labels.

If radiological convention is desired, we may want to consider adding an option, but that seems like it would make sense with a more significant refactor to simplify (or at least clarify) the visualization code.

Closes #559.

[codecov-io]

Codecov Report

Merging #564 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #564   +/-   ##
=======================================
  Coverage   94.32%   94.32%           
=======================================
  Files         177      177           
  Lines       24691    24691           
  Branches     2638     2638           
=======================================
  Hits        23290    23290           
  Misses        925      925           
  Partials      476      476

Impacted Files	Coverage Δ
nibabel/viewers.py	96.66% <ø> (ø)	⬆️

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[coveralls]

Coverage remained the same at 96.254% when pulling ee7d536 on effigies:fix/orthoview_lr_labels into b7eee37 on nipy:master.

[effigies]

Think this one should be pretty uncontroversial. Will merge tomorrow AM (EDT) unless there's an objection.