Notebook export to HTML needs work

[nikhilk]

Anything with script doesn't work.
--> we generally need to think of static HTML experience
--> we need a custom notebook convert that loads client-side dependencies
--> we should generate script that can detect there is no session, and not attempt to make calls to the kernel

Styling - converted HTML should be consistent w. authoring experience.

[gramster]

We have a bunch of improvements in this area including the session guard so this may be closeable.