demo: apply responsive design to demo page

Since already use bootstrap to demo page, we could layout components
by boostrap classes to instead of using hard-coded width.
demo: add case of connected list

connected list is also a good feature of ui-sortable.
add one more case to demo.
Merge branch 'master' of https://github.com/walkingice/ui-sortable into walkingice-master
fix(demo): disable sorting between examples
Merge pull request #303 from thgreasi/walkingice-master

demo: add example of connected lists