add triggers for challenges and stream

[proditis]

This PR does the following

• Trigger Before Delete on player
• Introduces echoctf player column
• Trigger after delete challenge
• trigger before delete challenge
• trigger after delete on stream
• trigger after delete on team_stream

Due to the way mariadb works triggers do not fire up for related data. These triggers make sure that the related operations are performed by individual delete commands and thus making sure the score of the player and their teams is accurate.