Use sqlite3.Row factory in Flaskr

As pointed out in issue #588 sqlite3.Row should be used instead of
using casting to dict(). Also altered the "Easy Querying" Patterns
example to include the more correct way to return rows as dicts.
Did not touch Tutorial examples ("Views"), as these are not up to
date with the current Flaskr code, and the "Show Entries" section
points out the "Easy Querying" section on how to convert to a
dict().
Merge pull request #625 from soulseekah/master

 Use sqlite3.Row factory in Flaskr (#588)