Something
Make selection widget respect order.
Import Tuple traitlet for Selection widget
Fix variable name
Fix readonly lock logic.
Don't magically convert values to a list of tuples.
Fix faulty interact tests
Typo fix
Selection test fix
Changed the display order of rich output in the live notebook to match that of nbconvert.  This makes more sense than the other way around due to the need for notebooks already shared on the web to remain consistant. Conversely local notebooks can simply be edited to match the new order.
add pre/post-save hooks

- `ContentsManager.pre_save_hook` runs on the path and model with content
- `FileContentsManager.post_save_hook` runs on the filesystem path and model without content

- use pre_save_hook for things like stripping output
- use post_save_hook for things like nbconvert --to python
`--script` triggers post_save hook with nbconvert
update `--script` behavior to use `nbconvert --to script`
docstring
load the per kernel kernel.js and kernel.css

As per discussion, each kernel can provide a file name kernel.js that
we try to load at kernel switching. If such a file exist we assume that
the kernel pathches the javasscript and that this javascript cannot be
unpatched, and further switching of the kernel cannot be undone without
reloading the page. (separate PR for UI)

if a kernel provide kernel.js, the it should consist into a AMD module
definition that uses require.js the module shoudl define a function name
`onload` that will be called at the appropriate moment before the kernel
starts.
Fix typos, rephrase english. Thanks Kyle.
adresses Min comments
Another widget promise bug fix
add an humanize function that prettify shortcut on macos
Add notion of actions to celltoolbar

modify toolbar.js to be able to deal with actions.

modify maintoolbar to deal with the new action architecture

add a way to triger notification widget hiding