Allow selecting multiple VMs

Feature request from issue #50 implemented for some VM operations
Made messagebox descriptions more specific by including VM name in them
Kill option is now always available, so it can be used in case of VM status mismatch
Added an error message if shortcut creation fails

Author: daviunic

86BoxManager/Program.cs

@@ -87,7 +87,7 @@ static void Main()
                 Process[] pname = Process.GetProcessesByName("86box");
                 if (pname.Length > 0)
                 {
-                    DialogResult result = MessageBox.Show("At least one instance of 86box is already running. It's not recommended that you run 86Box.exe directly outside of Manager. Do you want to continue at your own risk?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Warning);
+                    DialogResult result = MessageBox.Show("At least one instance of 86Box.exe is already running. It's not recommended that you run 86Box.exe directly outside of Manager. Do you want to continue at your own risk?", "Warning", MessageBoxButtons.YesNo, MessageBoxIcon.Warning);
                     if (result == DialogResult.No)
                     {
                         return;