fix(core): Caches DateTime.NowUtc (#548)

- [X] Caches DateTime.NowUtc on the game loop (not other threads)
- [X] Replaces all locations where it makes sense
- [X] Adds Min/Max for `IComparable` (TimeSpan, DateTimes, etc)

Closes #261

Projects/UOContent/Multis/Camps/BaseCamp.cs

@@ -66,7 +66,7 @@ namespace Server.Multis
 
             if (setDecayTime)
             {
-                m_DecayTime = DateTime.UtcNow + DecayDelay;
+                m_DecayTime = Core.Now + DecayDelay;
             }
 
             m_DecayTimer = Timer.DelayCall(DecayDelay, Delete);