Added resource detail page.

Added get_absolute_url method, url, view and
template for resource detail. Updated the
resource_text.txt file to reduced db hits.
refs #6 Added facebook share button to resource detail

page.
Added meta tags for facebook share button.

Added new setting to dev, staging and production
enviroments: "SITE_URL"
Merge pull request #20 from openrural/resource-detail

Resource detail page