Merge remote-tracking branch 'origin/Issue4149_TextExplorerFilter' into Issue4149_TestExplorerFilter

Author: IvenBach

Rubberduck.Core/UI/UnitTesting/TestExplorerViewModel.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.ComponentModel;
 using System.Globalization;
 using System.Linq;