Adding a regex based solution for enumerating files looking for multiple extensions at same time (#811)

* Adding a regex based solution for enumerating files looking for multiple extensions at same time. This should give better performance than enumerating over the same files multiple times looking for different patterns

* Adding a timeout value for regex per security recommendation

* Store the regex directly so we don't have to keep constructing it, also adding some logging and handling for exceptions when enumerating files

Vocaluxe/Base/CSongs.cs

@@ -348,8 +348,7 @@ namespace Vocaluxe.Base
                     {
                         if (Directory.Exists(path))
                         {
-                            files = files.Union(CHelper.ListFiles(path, "*.txt", true, true));
-                            files = files.Union(CHelper.ListFiles(path, "*.txd", true, true));
+                            files = files.Union(CHelper.ListTextFiles(path, true, true));
                         }
                     }
                 }