Provide error when adding more than 32 teams to a pool

[Jellest]

During ISBT Enschede 2017, a pool was made with more than 32 players. First 2 rounds went fine but no 3rd round was able to be made. This is because Tournia has put a max to 32 teams per pool.

Therefore, show a warinng when someone tries to add a 33rd team and prohibit that.