Support serving kernelspec resources

A long-standing TODO item for NB2KG was to add support for kernelspec
resources (kernel.js, kernel.css and logo-*).  This can't be accomplished
until JKG provides the endpoint such that specific resources can be fetched.

Author: kevin-bates

kernel_gateway/services/kernelspecs/handlers.py

@@ -3,6 +3,8 @@
 """Tornado handlers for kernel specs."""
 
 import notebook.services.kernelspecs.handlers as notebook_handlers
+import notebook.kernelspecs.handlers as notebook_kernelspecs_resources_handlers
+
 from ...mixins import TokenAuthorizationMixin, CORSMixin, JSONErrorsMixin
 
 # Extends the default handlers from the notebook package with token auth, CORS
@@ -12,3 +14,8 @@
     # Everything should have CORS and token auth
     bases = (TokenAuthorizationMixin, CORSMixin, JSONErrorsMixin, cls)
     default_handlers.append((path, type(cls.__name__, bases, {})))
+
+for path, cls in notebook_kernelspecs_resources_handlers.default_handlers:
+    # Everything should have CORS and token auth
+    bases = (TokenAuthorizationMixin, CORSMixin, JSONErrorsMixin, cls)
+    default_handlers.append((path, type(cls.__name__, bases, {})))