Convert StomachBehavior to a component/system + rejig body namespaces (#5249)

* Convert StomachBehavior to a component/system + rejig body namespaces

* test

* slightly more namespace changes

* remove

* Hello?????

* fuck you github test runner

* reviews

* oobsy!

Content.Server/Administration/Commands/AddEntityStorageCommand.cs

@@ -1,4 +1,3 @@
-using Content.Server.Body.Mechanism;
 using Content.Server.Body.Part;
 using Content.Server.Storage.Components;
 using Content.Shared.Administration;