Startup: load config before Main ctor

Allows specifying Dark mode in settings now.
Extracts reusable settings objects to PKHeX.Core (drawing/GUI stuff kept in WinForms).
Updating settings now refreshes backup paths/mgdb

PKHeX.Core/Editing/Program/SaveFileLoadSetting.cs

@@ -0,0 +1,22 @@
+namespace PKHeX.Core;
+
+/// <summary>
+/// Option to load a save file automatically to an editing environment.
+/// </summary>
+public enum SaveFileLoadSetting
+{
+    /// <summary>
+    /// Doesn't autoload a save file, and instead uses a fake save file data.
+    /// </summary>
+    Disabled,
+
+    /// <summary>
+    /// Loads the most recently created Save File in the usual backup locations.
+    /// </summary>
+    RecentBackup,
+
+    /// <summary>
+    /// Loads the most recently opened Save File path.
+    /// </summary>
+    LastLoaded,
+}