DB: Add table for ticks

[F30]

At the moment, we assume that actual start and end times for ticks are equal to the theoretical ones as computed from start time of the CTF and tick duration. Additionally, the current tick is stored in the "scoring_gamecontrol" table.

For improved error handling and better insights, it would be beneficial to have an extra table which stores the actual start and end time for each tick. All fields storing ticks, which are just integer values at the moment, should then be converted to Foreign Keys.

[F30]

Would also help for #66.