This callback enables code to update its metrics only when required. Needed this for SS14 since online admin count stats are not something I want to update on an "arbitrary" basis.
Tons of consideration and commenting for how this plays in with stuff like dotnet-counters. Added the metrics.update_interval CVar to act as a fallback for this event when dotnet-counters and such is in use.
* Removed the Interfaces folder.
* All objects inside the GameObjects subfolders are now in the GameObjects namespace.
* Added a Resharper DotSettings file to mark the GameObjects subfolders as not providing namespaces.
* Simplified Robust.client.Graphics namespace.
* Automated remove redundant using statements.
