ignore more stuff

repeat the disclaimer about jlb4 & nb7 in the toplevel README

fix and close #646

blind attempt at fixing doc build

add a disclaimer, first thing on the landing page

clarify that the classic version is obsolete and redirect jlab users to jupyterlab-rise

no longer reference header-footer.ipynb as this file is now a .md

fix a confusing comparison - apparently no change in behaviour

Merge pull request #631 from pitmonticone/master

Fix a few typos in examples and docs

publish as 5.7.2.dev2

Relayout button

Merge pull request #626 from multimeric/fix-625

Fix 625

minor tweaks in the doc for fewer warnings