Validate slider value, when limits change
The value of slider changes in frontend, and readout, but not in python obj.
Sending data back to python object after slider values change
A comma after `this.touch`
Add EventfulList and EventfulDict trait types.
Address review comments @takluyver
Added on_events convinience method
Use ternary operator for callback registration
kwarg on_events and hardcoded callbacks
s/this/self
Default view should be the base widget view class
Add failing test for issue gh-6282
Cast module name to bytes for Py2 ModuleType constructor

Closes gh-6282
Embrace flexible box model
Added baseline and stretch
Renamed *Widget to *,
depracted old names.
Fix interact tests for rename
adding hbox and vbox

Conflicts:
	IPython/html/static/widgets/js/widget_container.js
	IPython/html/widgets/widget_container.py
Make HBox and VBox helper functions
Added some doc strings on the widgets.
Also address the comments Matthias left me.