Changes widget's name, and adds bootstrap-wysihtml5 to the demo.

1. Changes widget's name to Wysihtml5TextareaWiget.
2. Rearrange static files' directories.
3. Adds twitter_bootstrap.py to the demo:
   Extends Wysihtml5TextareaWidget with bootstrap-wysihtml5.
4. Adds twitter-bootstrap look&feel to the demo site,
   a ModelForm for the Article model and a generic view
   CreateView to add new Article instances.