Convert newlines to <br /> in messages to source's

Hopefully fixes #521 by converting newline character to <br /> tags in messages before being displayed on the /lookup page.
Maybe I'm reading this the wrong way, but from what I see the escaped Markup object from jinja2.escape is being converted to a unicode string in the .join() expression.

If that string is returned by the filter directly then it's gonna be escaped again (its not marked as unsafe). As far as I see, it does need be converted back to a Markup object before returing or it will be escaped again.

The object representation can be seen in this gist - https://gist.github.com/DonnchaC/2bbf56521c35eef1523f