Don't set "no cache" headers in Flask

These headers are set by Apache, according to the {source,document}.site
configuration files, in production. They are unnecessary in development.
Therefore, setting these headers in Flask is redundant (and could potentially
cause conflicts with the Apache configuration, especially if they diverge in
the future).
Merge pull request #336 from garrettr/feature/remove-after-request

Don't set "no cache" headers in Flask