Grouped activities

[Daniel Besse]

Multisport activities are split by Strava and thus displayed as many activities in 3r. We can keep it as is but it would be nice to also have a way of viewing the "total"/combined activity to have the global picture

[Daniel Besse]

1. Removing some of this swimrun spam on the calendar
2. Having the possibility of analyzing one part with pre-fatigue from another (eg: run after bike in tri is not the same as run alone)