"Flavor" extension

[Please treat this issue name as provisional.]

As part of the one click project, we are exploring ways to allow people to install a set of extensions and configuration that meet a particular use case, e.g. sports clubs, or event organisers, similar in nature to Drupal distributions.

cc @totten, @ufundo, @alainb @jaapjansma, @jgleeson - I think you all have expressed an interest in this.