Add support for tugboat

Here's the patch.

And here's a patch for 7.x

I made some changes to the D7 file (hopefully it works). Here's the resulting file.

Trying with a different config.yml - it will be interesting to see if this works :)

I've got tugboat loading, but POST won't work. I sent a request to the Tugboat Slack to see if anybody knows what's wrong.

Merging the MR. We can currently check that the banner loads and that the options on the admin page loads correctly. What we can't do yet, is POST forms due to a Tugboat issue. I'm working with the Tugboat team to get this sorted.