Bumping to knex 0.5 and bookshelf 0.6

So this looks like it's broken because it logs some new errors in the import tests about the slug not being unique - @sebgie I'm not sure if this is related at all to what you were doing with the transactions...

If anyone seems to know what might be causing these issues, I'll see if I can help debug... I was having a little trouble following the test code at first glance.

I figured it'd be good to move up to the latest soon to see if any of the latest tweaks for PostgreSQL have helped, and make it easier to upgrade for new fixes there, re: #1555.

There's also a really, really bare bones [migration api](http://knexjs.org/#Migrate) if anyone is interested.