Use path+filesize instead of xxHash for frame count caching

Code/Data/PseudoUniqueFile.cs

@@ -0,0 +1,20 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Flowframes.Data
+{
+    class PseudoUniqueFile
+    {
+        public string path;
+        public long filesize;
+
+        public PseudoUniqueFile (string pathArg, long filesizeArg)
+        {
+            path = pathArg;
+            filesize = filesizeArg;
+        }
+    }
+}