Extremely basic game ticker. (#126)

You can theoretically restart the round (resetting the map) now, but it breaks very badly if a client is connected due to various edge cases/race conditions.

Content.Server/Interfaces/GameTicking/IGameTicker.cs

@@ -0,0 +1,23 @@
+using Content.Server.GameTicking;
+using SS14.Shared.Interfaces.GameObjects;
+using SS14.Shared.Timing;
+
+namespace Content.Server.Interfaces.GameTicking
+{
+    /// <summary>
+    ///     The game ticker is responsible for managing the round-by-round system of the game.
+    /// </summary>
+    public interface IGameTicker
+    {
+        GameRunLevel RunLevel { get; }
+
+        void Initialize();
+        void Update(FrameEventArgs frameEventArgs);
+
+        void RestartRound();
+        void StartRound();
+        void EndRound();
+
+        IEntity SpawnPlayerMob();
+    }
+}