Merge pull request #4086 from ivanov/missing-errno

fix missing errno import
manual rebase base/handlers.py
manual rebase notebook/handlers.py
manual rebase notebookapp.py
manual rebase services/kernels/
manual rebase notebooks web services
manual rebase - add sessions web service
manual rebase static/notebook/js files
manual rebase static/services (add session.js)
manual rebase static/tree/
manual rebase html notebook templates
manual rebase tree/handlers.py
fixing some bugs after rebase
fixing path redirects, cleaning path logic
delete debug comment
fix restart/interrupt kernel buttons
fix kill_and_exit button in notebook
fixed shutdown button refresh on dashboard
Add 'patch' to session & notebook, rename working
allow rename in subdirectory notebooks