Fixed widget imports for Python3
Fix slider orientation change, value-handle-offset bug
Made TextArea and TextBox views compatable with disabled property
Fixed slider orientation bug for IntSliderView (already done for float)
...related to commit before last...
Made checkbox and togglebutton compatable with disabled property
Made RadioButtons and ToggleButtons views compatible with disabled property
Added ability to specify the element that gets style in a view
when no jquery selector is provided (default).
Added selected_index property to TabView
More relative imports, Travis w/ Py3.3
Add basic widget.js tests
Allow parent to be set after construction...
But still must be set before display call
Added `visible` property to all widgets
Remove text repr of js includes.
Added add_class and remove_class methods.
Set default element to be styled in built-in views
Fixed button on_click handler so it's initiated on instanciation
Fixed callback mapping for widget spawned widgets
Decoupled cell_index from widget model code.
Fixed & separated output_area -> widget_area logic
Fixed comment in widget.js