ensure k3d is the backend for html export, but that this change in ba…

…ckend is scoped

k3d seems like a good choice for html as k3d provides standalone HTML/JS rendering capabilities: https://github.com/K3D-tools/K3D-jupyter
it is one of the options for a jupyter notebook too. see https://vedo.embl.es/docs/vedo.html

brainrender/render.py

@@ -289,6 +289,7 @@ def export(self, savepath):
         """
         logger.debug(f"Exporting scene to {savepath}")
         _backend = self.backend
+        _default_backend = vsettings.default_backend
 
         if not self.is_rendered:
             self.render(interactive=False)
@@ -314,7 +315,7 @@ def export(self, savepath):
         )
 
         # Reset settings
-        vsettings.notebookBackend = None
+        vsettings.default_backend = _default_backend
         self.backend = _backend
 
         return str(path)