Allow to view single entry via url.

#8
Rename entry's content attribute to body.

Content is kind of a reserved or rather already used word for example
in controller and sometimes can cause issues.
Order all entries by id desc by default.
Entry.all now returns records sorted by id desc by default.
Extend DS.ActiveModelSerializer since that's what we're using.
Add links for content entries in rss feed.
Add title class to link instead of surrounding div.