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
Add support for notebook server extensions

As some people may be tiring of my pointing out, it seems strange that
we have extension points for the JS and the kernel, but none for the
notebook server.

For cite2c, I want to add a handler which can serve a directory of style
files for use by the nbextension part.
Rename extensions -> server_extensions
Note that extension API is experimental
Add extension traitlet to force dotted names
Import extension traitlet in top-level nbconvert
Rename Extension to FilenameExtension