Updated activities overview design

We have a new set of designs for the activities overview, which are the outcome of a long-running programme of work by the design team. The latest iteration of these designs can be found, in the os-mockups repository.

This ticket is intended as a meta tracking issue relating to the new design. Specific issues, either for missing implementation steps or for issues with the implementation, should be filed separately (please do mention this issue in any new tickets though).

More general design issues should be reported directly against os-mockups.