refactor out most of TransitionalFileLocator. Almost done with new stateful is-liberated paradigm

FileManager/BackgroundFileSystem.cs

@@ -9,7 +9,14 @@ using System.Threading.Tasks;
 
 namespace FileManager
 {
-    class BackgroundFileSystem
+    /// <summary>
+    /// Tracks actual locations of files. This is especially useful for clicking button to navigate to the book's files.
+    /// 
+    /// Note: this is no longer how Libation manages "Liberated" state. That is not statefully managed in the database.
+    /// This paradigm is what allows users to manually choose to not download books. Also allows them to manually toggle
+    /// this state and download again.
+    /// </summary>
+    internal class BackgroundFileSystem
     {
         public string RootDirectory { get; private set; }
         public string SearchPattern { get; private set; }