Rebranding for 2019

[i-like-robots]

We are still using the original description of the project from when it was first started:

x-dash is an experiment in building new shared front-end components for FT.com and the FT Apps. A detailed introduction is available in Google Slides.

Now that x-dash is being used in production and is no longer flagged as experimental (#261) we should revisit this using the information and perspective we now have about how to use x-dash effectively.

I think an updated introduction to x-dash should answer the question "what is this?" as well as "why should I use this?" and be crafted to suit both a technical and non-technical audience.