State intent to solve problem of requiring assets

Libraries, and by extension kernels, have static assets that are required in frontends such as the notebook, thebe, hydrogen, and dashboards..

This issue continues to come up over and over without a total solution. At the very least I'd like for us to put it on the roadmap and acknowledge that we will solve it.

Initial (old) proposal/discussion: jupyter/notebook#116
Related: jupyter/notebook#839

As it applies to Thebe, they currently have to bundle

* all notebook js (not tied to kernel)
* ipywidgets js (tied to kernel)
* thebe itself

Each thebe release has to strictly specify the version of notebook, ipywidgets, in addition to thebe itself, and is incompatible with other versions.

Discussion from the Spring Jupyter Dev Meeting 2016: https://jupyter.hackpad.com/Spring-2016-Dev-Meeting-h0y1TIAWxz1#:h=Kernel-Static-Resources

README.md

@@ -217,6 +217,10 @@ planned. However, we plan to:
 
 ## Notebook document
 
+## Kernel specification
+
+Implement a way for static resources (js, css, images, etc.) to be fetched based on the kernel for use by frontends (notebook, thebe, etc.).
+
 ## Message specification
 
 ## Community Pipeline