Redo activities so they are applied to correct challenge regardless

[plinck]

Is your feature request related to a problem? Please describe.

Describe the solution you'd like
I want activities to be associated with users - not teams or challenges. Also, the user should be able to switch which team an activity is associated with. Would be great if admin could do that. Also, would be great (for now before this feature is implemented) if you could change challenge AND team for a specific activity.

Describe alternatives you've considered

Additional context

[plinck]

Give admin ability to select all members in challenge and all members on team

[plinck]

Send message to user if their workout was rejected or accepted from starve. Messaging will be very cool