feature: welcome screen, toolbar & chore: more docs

CarManagerV3/Forms/Welcome.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Data;
+using System.Drawing;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Forms;
+
+namespace CarManagerV3.Forms
+{
+    public partial class Welcome : Form
+    {
+
+        // callback functions
+        // Open file
+        public Action OpenFileCallback;
+
+        public Action NewFileCallback;
+
+
+        public Welcome()
+        {
+            InitializeComponent();
+        }
+
+        private void Welcome_Load(object sender, EventArgs e)
+        {
+
+        }
+
+        private void btnOpenFile_Click(object sender, EventArgs e)
+        {
+            this.OpenFileCallback();
+        }
+
+        private void btnExit_Click(object sender, EventArgs e)
+        {
+            Environment.Exit(0);
+        }
+
+        private void btnNewFile_Click(object sender, EventArgs e)
+        {
+            this.NewFileCallback();
+        }
+    }
+}