Remove legacy azure nbmanager
handle image size metadata in nbconvert html
Remove remaining refs to the Azure NB Manager
Add documentation for removal
Add pointers to simple nb manager and bookstore.
Change wording to say that the azure nb was actually removed
fix a link that was broken
Merge pull request #5150 from ivanov/fix-fonnesbeck-link

fix a link that was broken
fix IPython typo, closes #5155
Merge pull request #5156 from ivanov/fix-5155

fix IPython typo, closes #5155
remove append_json reference

we never had such a method
Merge pull request #5095 from minrk/image-size

handle image size metadata in nbconvert html
Merge pull request #5159 from ivanov/oops-json

remove append_json reference
Merge pull request #5089 from rgbkrk/azure_out

Remove legacy azure nbmanager