Add a footer variant that provides a way to credit organisations for their contributions

For example, to recognise code4iati's contribution to the Dashboard through the Analytics project, for ODS/code4iati on IATI Tables, and in the future PWYF for a potential bit of Dashboard code.

I kinda envisage this as either a specific variant of the Additional Information layer, or a slim full-width component that acts as a bit of a logo wall type thing