webglapp: rename toggle_zplane to toggleZplane for consistency with the naming convention followed by the other toggle functions.
webglapp: rename toggle_zplane to toggleZplane for consistency
with the naming convention followed by the other toggle functions.

htem/CATMAID,fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID,htem/CATMAID,fzadow/CATMAID,fzadow/CATMAID,htem/CATMAID