CSS: bundle everything into one file

Giraffe should provide one **.css** file that includes all CSS for all of its components.

There are consuming apps which may want to use a single **.css** file from their libraries in order to generate assets during their build processes. For example, the `ui` repository pulls in a single **index.css** for one of its other libraries (Clockface). By doing this, the `ui` repository is able put any assets that are included in the **.css** files into a folder for static assets during build time. Giraffe should do the same thing.

Doing this may have an impact on performance, so this request should also be considered from an performance standpoint.

Start by reviewing how Giraffe currently produces its CSS and compare the requested single index.css pattern with the ui repository's Clockface integration. Confirm that one output file contains all component CSS and assess the performance impact before considering the work complete.

Written by the indexing model from the issue text.