Port to 2.0

Fix up a problem where if no published_at date, display will fail.
Not sure if this is the right solution. Confused by the existence of "published_at" and "visible"
flag.
Populate published date when creating a BlogEntry.
Add date to recent blog entries widget.
Stay on edit page when updating a blog entry in the admin.
Update Versionfile.
Merge pull request #1 from rterbush/2-0-0-beta

Port to 2.0
Update Gemfile.