send idle/busy on all shell messages

Instead of just those that execute code.
This means that kernel_info_request triggers busy/idle,
allowing clients to check IOPub channel status without executing code.
Set axis background to transparent in inlinebackend

Fixes #5727, related to #4608
set busy/idle around every message

not just shell
Updated license to include CC BY 4.0 for documentation, examples, and other materials
Added examples to BSD, and added links to online versions of CC-BY
Moved the list of links of the CC-BY licenses below (I could not get RST to render correctly)
Check for pids when listing nbserver processes
Use check_pid from utils in IPython.parallel
Add support for different kernel specs to kernels REST API
Add kernel name to sessions REST API

Also, some refactoring so that the relationship between session, kernels
and notebooks is managed in the SessionManager, not in the HTTP
handlers.
Update JS for kernels and sessions APIs
Delete session rather than killing kernel in test cleanup
Fix JS syntax
Solving #5997: instances of WidgetView (that are not instances of DOMWidgetView) do not trigger widget_area.show anymore.
Remove / from route of TreeRedirectHandler.

When base_url is set, navigating to http://{url}/{base_url} returns 404
This is due to the TreeRedirectHandler only picking up
http://{url}/{base_url}/ and the trailing slash handler being set to
{base_url}/.*/.

This change will cause http://{url}/{base_url} to correctly redirect to
http://{url}/{base_url}/tree, as expected.
Add default_kernel_name class level variable
Merge pull request #6117 from thetestpeople/base_url-path-slash

Remove / from route of TreeRedirectHandler.
Merge pull request #6026 from takluyver/kernelspec-rest-launching

Kernelspecs in REST API for kernels and sessions
Only allow iframe embedding on same origin.
Incompatibility notice on iframe embedding