Move to 4.x notebook as the minimum requirement

[parente]

We put off moving the code in this repo to supporting the post-Big Split version of the notebook until we understood the future intersection of the work here with the future version of notebook based on Phosphor. After meeting with @sccolbert, @ellisonbg and others about that topic, we agreed that pushing the dashboard layout implementation into jupyter/notebook ahead of the phosphor port of notebook doesn't make much sense: it'll all need to be redesigned and reimplemented later in the context of the more pluggable notebook. That said, it looks like the jQuery-based notebook will be around for a while longer as work proceeds on the Phosphor-based UI encompassing all the current pieces of Jupyter Notebook.

In the interest of keeping the dashboard (and declarative widgets) concepts relevant along the way, we should invest the time in making them 4.x compatible. I suspect that by 4.x compatible, I really mean "any version post-Big Split compatible" since even if the notebook version numbers jump to 5.x, 6.x, etc. major UI changes aren't likely to land in the classic, jQuery impl, but rather in the PhosphorJS one. So, hopefully, migrating the extensions should be a one time cost.

All that said, we agreed that once there's some flavor of Phosphor in Jupyter Notebook, we will collaborate on how dashboards and other incubator features start to plug into that new foundation.

[parente]

Things known to be broken so far:

• setup.py install fixed: updated and tested
• Paths of config files in makefile fixed: updated and tested
• nbconvert flags (--quiet) fixed: use --log-level
• nbformat.notebooknode.NotebookNode object has no attribute 'layout' when running nbconvert (context is different now?) (bug in master, opened in 500 error (sometimes) when converting to dashboard #92)
• Strange errors before moving to thebe master branch commit w/ 4.0 support, bumped to latest thebe
• IPython.OutputArea no longer defined, fixed: dbl click now adds css img.unconfined rule which we need to reset to prevent double click overflowing grid cell
• Have to wait for kernel_ready.Kernel before executing code now else execute requests are dropped (used to queue?) (bug in master, fixed in PR Race condition between execute all in thebe and kernel ready #85)
• demo changes (ipywidgets JS paths, ipywidgets top level package, traitlets top level package) fixed: scotch notebook, all test/* notebooks, pending decl widget bump to 4.x compat to test all others
• focus rects around cells in deployed dashboard fixed: transparent border for selected cells

[parente]

All known bugs handled. Putting in stasis pending decl widget update to 4.x too.

[parente]

Merged into master on Friday after lots of manual demo testing plus all green on Travis.