Gas tanks and masks (#2409)

Co-authored-by: a.rudenko <creadth@gmail.com>
Co-authored-by: creadth <creadth@users.noreply.github.com>
Co-authored-by: DrSmugleaf <DrSmugleaf@users.noreply.github.com>

Content.Server/Interfaces/IGasMixtureHolder.cs

@@ -5,5 +5,20 @@ namespace Content.Server.Interfaces
     public interface IGasMixtureHolder
     {
         public GasMixture Air { get; set; }
+
+        public void AssumeAir(GasMixture giver)
+        {
+            Air.Merge(giver);
+        }
+
+        public GasMixture RemoveAir(float amount)
+        {
+            return Air.Remove(amount);
+        }
+
+        public GasMixture RemoveAirVolume(float ratio)
+        {
+            return Air.RemoveRatio(ratio);
+        }
     }
 }