feature/491: listing page for walkthroughs

* created a teaser view for walkthroughs
  * with edit link, if user has the permission
* themed the small widget for make it usable
fetaure/491: fixing problems reported by reviewer.

* use the l() function
* use the format_date() function
* check permission in preprocess.
feature/491: fixing problems reported by reviewer.
feature/491: fixing reported errors.
Merge pull request #73 from csanyiarpad/feature/491-walkthrough-listing-page-theming

feature/491: listing page for walkthroughs