Add about dialog in Notebook Help Menu.

This allow to get info on version of IPython when running remotely.
The about dialog also send a kernel info request and display the banner
which is useful for non-python kernel that don't match IPython version
Move language info from kernelspec to kernel_info_reply
Use language_info instead of kernelspec in nbconvert
Remove language info from kernelspec test
Update docs about kernelspecs and kernel_info_reply
Add language_info field to message spec tests
Basic infrastructure for terminal page
Terminal basically working

Still need to deal with things like authentication
Multiple terminals and conditional initialisation
Initial REST API for terminals
Add authentication for terminal websockets
Put terminal handlers under base_url
Don't load html.terminal for tests if terminado not installed
Use relative URL for redirect in NewTerminalHandler
Add term.js to package data for installation.
recompute dummy size dynamically + styling in css
HTML fix
Add mention of terminals in whatsnew
Add comment explaining 1.02 factor
Move terminal CSS into LESS file