Makes map vote and roundstart smart about player count. (#5418)

* Makes map vote and roundstart smart about player count.
No more Saltern with 30 players, or Knight Ship with 50.

* a typo

* Address reviews.

* Localized.

Content.Server/Maps/IGameMapManager.cs

@@ -0,0 +1,68 @@
+using System.Collections.Generic;
+
+namespace Content.Server.Maps
+{
+    /// <summary>
+    /// Manages which station map will be used for the next round.
+    /// </summary>
+    public interface IGameMapManager
+    {
+        void Initialize();
+
+        /// <summary>
+        /// Returns all maps eligible to be played right now.
+        /// </summary>
+        /// <returns>enumerator of map prototypes</returns>
+        IEnumerable<GameMapPrototype> CurrentlyEligibleMaps();
+
+        /// <summary>
+        /// Returns all maps that can be voted for.
+        /// </summary>
+        /// <returns>enumerator of map prototypes</returns>
+        IEnumerable<GameMapPrototype> AllVotableMaps();
+
+        /// <summary>
+        /// Returns all maps.
+        /// </summary>
+        /// <returns>enumerator of map prototypes</returns>
+        IEnumerable<GameMapPrototype> AllMaps();
+
+        /// <summary>
+        /// Attempts to select the given map.
+        /// </summary>
+        /// <param name="gameMap">map prototype</param>
+        /// <returns>success or failure</returns>
+        bool TrySelectMap(string gameMap);
+
+        /// <summary>
+        /// Forces the given map, making sure the game map manager won't reselect if conditions are no longer met at round restart.
+        /// </summary>
+        /// <param name="gameMap">map prototype</param>
+        /// <returns>success or failure</returns>
+        void ForceSelectMap(string gameMap);
+
+        /// <summary>
+        /// Selects a random map.
+        /// </summary>
+        void SelectRandomMap();
+
+        /// <summary>
+        /// Gets the currently selected map, without double-checking if it can be used.
+        /// </summary>
+        /// <returns>selected map</returns>
+        GameMapPrototype GetSelectedMap();
+
+        /// <summary>
+        /// Gets the currently selected map, double-checking if it can be used.
+        /// </summary>
+        /// <returns>selected map</returns>
+        GameMapPrototype GetSelectedMapChecked(bool loud = false);
+
+        /// <summary>
+        /// Checks if the given map exists
+        /// </summary>
+        /// <param name="gameMap">name of the map</param>
+        /// <returns>existence</returns>
+        bool CheckMapExists(string gameMap);
+    }
+}