Set axis background to transparent in inlinebackend

Fixes #5727, related to #4608
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
Make Container widgets take children as the first positional argument

This makes creating containers less cumbersome: Container([list, of, children]), rather than Container(children=[list, of, children])
Container assumes the children attribute is not None

Thanks to @SylvainCorlay for pointing this out.
Added jquery in define
remove pagemain.js

It does not seem to be usefull anymore.

The different main.js of /tree /notebook /etc do create an instance of
`page` themselves, error pages do have hardcoded styles that show header
and sites.
Merge pull request #6064 from Carreau/fix-5727

Set axis background to transparent in inlinebackend
Merge pull request #6169 from tarzzz/fix-requirejs

Added jquery in define
Merge pull request #6099 from takluyver/check-nbservers-pid

Check process existence when listing nbserver processes
Merge pull request #6074 from dsblank/master

Updated license to include CC BY 4.0 for documentation
Merge pull request #6174 from Carreau/pagemain

remove pagemain.js
Merge pull request #6153 from jasongrout/container-children-arg

Make Container widgets take children as the first positional argument
Merge remote-tracking branch 'upstream/master'