FileSystemContainers need to .Load and fire .ContainerChanged on filter

- Issue MatterHackers/MCCentral#2455
Search not functioning in Downloads folder

Library/Providers/FileSystem/FileSystemContainer.cs

@@ -102,6 +102,8 @@ namespace MatterHackers.MatterControl.Library
 				if (keywordFilter != value)
 				{
 					keywordFilter = value;
+					this.Load();
+					this.OnContentChanged();
 				}
 			}
 		}