Revert PluginCore use of event listening for current LogMonitor state (#64)

The order that listeners get notified isn't deterministic and as a result plugins which read the current state from PluginCore during the handling of a state change event may read a stale state resulting in unexpected results. PluginCore now reads a property directly from LogMonitor to avoid such inconsistencies.

ObservatoryCore/LogMonitor.cs

@@ -38,6 +38,13 @@ namespace Observatory
 
         #endregion
 
+        #region Public properties
+        public LogMonitorState CurrentState
+        {
+            get => currentState;
+        }
+        #endregion
+
         #region Public Methods
 
         public void Start()