webglapp: destroy_data must also delete the meshes and the missing sections.
webglapp: destroy_data must also delete the meshes and the missing sections.

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