Anticipate obstacles to removing Turbolinks

There are lots of parts of the GitLab application that rely on Turbolinks in very subtle ways.

Some discussion already happened here: https://gitlab.com/gitlab-org/gitlab-ce/issues/18673

Before digging into removing it, it would be worth trying to anticipate some of the obstacles that are likely to pop up.

I ( @brycepj ) will be experimenting with this, but any pointers and/or warnings would be much appreciated.