Change folderbrowser to openfile, select main instead

- Open file => main.dat will load the parent folder
- Allow dropping of main.dat (loads the parent folder)
- Shift clicking still behaves the same way
- Handle command line arguments to auto-load savedata from arg indexes >=1

Closes #37 ; unsure on licensing & mono compatibility, less dependencies

NHSE.WinForms/Main.Designer.cs

@@ -38,7 +38,7 @@ private void InitializeComponent()
             this.B_Open.Name = "B_Open";
             this.B_Open.Size = new System.Drawing.Size(306, 121);
             this.B_Open.TabIndex = 0;
-            this.B_Open.Text = "Open Folder";
+            this.B_Open.Text = "Open main.dat\r\n\r\nOr...\r\n\r\nDrag&&Drop folder here!";
             this.B_Open.UseVisualStyleBackColor = true;
             this.B_Open.Click += new System.EventHandler(this.Menu_Open);
             // 

NHSE.WinForms/Main.cs

@@ -20,6 +20,10 @@ public Main()
             WindowState = FormWindowState.Minimized;
             Show();
             WindowState = FormWindowState.Normal;
+
+            var args = Environment.GetCommandLineArgs();
+            for (int i = 1; i < args.Length; i++)
+                Open(args[i]);
         }
 
         private static void Open(HorizonSave file) => new Editor(file).Show();
@@ -56,9 +60,15 @@ private void Menu_Open(object sender, EventArgs e)
                     return;
                 }
             }
-            using var fbd = new FolderBrowserDialog();
-            if (fbd.ShowDialog() == DialogResult.OK)
-                Open(fbd.SelectedPath);
+
+            using var ofd = new OpenFileDialog
+            {
+                Title = "Open main.dat ...",
+                Filter = "New Horizons Save File (main.dat)|main.dat",
+                FileName = "main.dat",
+            };
+            if (ofd.ShowDialog() == DialogResult.OK)
+                Open(ofd.FileName);
         }
 
         private static void Open(string path)
@@ -67,7 +77,7 @@ private static void Open(string path)
             try
             #endif
             {
-                OpenSaveFile(path);
+                OpenFileOrPath(path);
             }
             #if !DEBUG
 #pragma warning disable CA1031 // Do not catch general exception types
@@ -79,6 +89,25 @@ private static void Open(string path)
             #endif
         }
 
+        private static void OpenFileOrPath(string path)
+        {
+            if (Directory.Exists(path))
+            {
+                OpenSaveFile(path);
+                return;
+            }
+
+            var dir = Path.GetDirectoryName(path);
+            if (dir is null || !Directory.Exists(dir)) // ya never know
+            {
+                WinFormsUtil.Error("Unable to open the folder that contains the save file.",
+                    "Try moving it to another location and opening from there.");
+                return;
+            }
+
+            OpenSaveFile(dir);
+        }
+
         private static void OpenSaveFile(string path)
         {
             var file = new HorizonSave(path);