Explorer: Show data for the current system only (#86)

Resolves #63

This behavior is suppressed during batch reads.

ObservatoryExplorer/ExplorerSettings.cs

@@ -86,6 +86,9 @@ namespace Observatory.Explorer
         [SettingDisplayName("Enable Custom Criteria")]
         public bool EnableCustomCriteria { get; set; }
 
+        [SettingDisplayName("Only Show Current System")]
+        public bool OnlyShowCurrentSystem { get; set; }
+
         [SettingDisplayName("Custom Criteria File")]
         [System.Text.Json.Serialization.JsonIgnore]
         public System.IO.FileInfo CustomCriteria {get => new System.IO.FileInfo(CustomCriteriaFile); set => CustomCriteriaFile = value.FullName;}