Healing component and Medkit (#143)

Medkit to heal yourself and your buddy
known issues:
- [ ] it doesn't restore screen effects that happens when health status go into crit and dead

Content.Server/EntryPoint.cs

@@ -102,6 +102,8 @@ namespace Content.Server
             factory.Register<ThrownItemComponent>();
             factory.Register<MeleeWeaponComponent>();
 
+            factory.Register<HealingComponent>();
+
             factory.Register<HandheldLightComponent>();
 
             factory.Register<ServerStorageComponent>();