fixup positional arg parsing in notebook app

- `ipnb .` triggers override of sub-config, even when the parent isn't changed
- `ipnb /path/nb.ipynb` sets notebook_dir to `/path`
write config instead of direct assignment from the command-line

Gross.
Changed children list to CTuple.

Also removed some unused refences in the widget code
and added support for tuples in the pack/unpack code.
use Tuple, not nonexistent CTuple
allow setting Tuple traitlet with list

matches traits behavior
s/CTuple/Tuple
Merge pull request #14 from minrk/cast-tuple

Cast from list in Tuple traitlet
don't check shape of ContainerWidget.children
remove incorrect is instance check in children_changed
Merge pull request #15 from minrk/ctuple

fix validation of ContainerWidget.children
don't validate ContainerWidget.children

just use a plain Tuple, so we don't have to define a new Trait
Merge pull request #16 from minrk/more-ctuple

don't validate ContainerWidget.children
don't forget base_url when updating address bar in rename
Merge pull request #5231 from minrk/rename-base-url

don't forget base_url when updating address bar in rename
Merge pull request #5221 from jdfreder/ctuple

Change widget children List to Tuple.
get _ipython_display_ method safely

use the same method we use for `_repr_foo_`
DOC : modified docs is HasTraits.traits and HasTraits.class_traits

 - change list -> dict to reflect what the code does
 - clarified how kwargs work (instead of just referencing enthought.traits).
 - fix classes -> class' spelling
Merge pull request #5234 from tacaswell/doc_hastraits.traits

DOC : modified docs is HasTraits.traits and HasTraits.class_traits
Merge pull request #5229 from minrk/safe-get-ipdisplay

get _ipython_display_ method safely
Merge pull request #5216 from minrk/notebook-dir-cli

fixup positional arg handling in notebook app