Adding Appcues integration.

Let me know if you have questions. I ended up changing files that I feel like should be auto-generated in order to get some tests passing.

Icons and brand assets located at https://github.com/appcues/brand:

[Appcues square logo - SVG](https://raw.githubusercontent.com/appcues/brand/master/mark-square.svg)
[Appcues square logo - PNG](https://raw.githubusercontent.com/appcues/brand/master/mark-square.png)
[Appcues square logo 2x - PNG](https://raw.githubusercontent.com/appcues/brand/master/mark-square@2x.png)