[#68943112] add a player to a team (web gui)
fix broken test
error check on Team model
change HTTP return code on errors
refactor controller - error handling
error handling when removing a player from a team
add default_serializer_options
[#71639702] remove dropdown player list menu when there is no unassigned players after adding a player to a team
change response body for POST /api/teams/:id/add_player/:player_id /api/teams/:id/remove_player/:player_id
[#71641562] update team player list after successfully adding a player to a team