Move relations from Player to Game_Player #22

At this moment, Player_Caught_Player, Player_Found_Player, and Notification_Player have relations with the Player table. However, the actions that these tables represent (Notifying, catching, and finding) all happen within the context of a game. Therefore, these relations should point at Game_Player, istead of Player.

Changes:

Player table renamed to User
Add Id to Game_Player
Replace PlayerId in Notification_Player with Game_Player_Id
Replace PlayerId in Player_Found_Objective with Game_Player_Id
Replace CatchingPlayerId in Player_Caught_Player with Game_Player_Id
Replace CaughtPlayerId in Player_Caught_Player with Game_Player_Id
Make clear in diagram that Game_Player Role defaults (to Role.none)

The names of the associationtables were not changed, because for instance Notification_Game_Player could be confused for a theeway association between Notigication, Game, and Player. Furthermore, The Player table is renamed to User, so Player only references Game_Player

Solved in commit b57d91d37c