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.Shared/GameObjects/EntitySystems/ExamineSystemShared.cs

@@ -1,5 +1,4 @@
-using System;
-using Content.Shared.GameObjects.Components.Mobs;
+using Content.Shared.GameObjects.Components.Mobs;
 using Content.Shared.Utility;
 using JetBrains.Annotations;
 using Robust.Shared.Containers;