Typo, redundant string interpolation, namespaces and imports cleanup (#2068)

* Readonly, typos and redundant string interpolations

* Namespaces

* Optimize imports

* Address reviews

* but actually

* Localize missing strings

* Remove redundant vars

Content.IntegrationTests/Tests/GridTileLookupTest.cs

@@ -1,4 +1,3 @@
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading.Tasks;
@@ -6,7 +5,6 @@ using NUnit.Framework;
 using Robust.Server.GameObjects.EntitySystems.TileLookup;
 using Robust.Shared.Interfaces.GameObjects;
 using Robust.Shared.Interfaces.Map;
-using Robust.Shared.Log;
 using Robust.Shared.Map;
 using Robust.Shared.Maths;