Add ability to run plugin manager as modal window

src/PackageManager.UI/PackageManager.UI.csproj

@@ -5,6 +5,7 @@
     <AssemblyName>PackageManager.UI</AssemblyName>
     <TargetFramework>net461</TargetFramework>
     <ApplicationIcon>Views\Assets\box-search-result.ico</ApplicationIcon>
+    <StartupObject>PackageManager.Program</StartupObject>
   </PropertyGroup>
 
   <ItemGroup>

src/PackageManager.UI/Program.cs

@@ -0,0 +1,48 @@
+using System;
+using System.Threading;
+using System.Diagnostics;
+using System.Linq;
+using System.Runtime.InteropServices;
+
+namespace PackageManager
+{
+    public static class Program
+    {
+        private const string ApplicationKey = "5CFB158B-8346-4588-926D-99006A5195B6";
+        private const int RestoreWindowCommandCode = 0x09;
+
+        [DllImport("user32.dll")]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);
+
+        [DllImport("user32.dll")]
+        private static extern IntPtr SetForegroundWindow(IntPtr hWnd);
+
+        [STAThread]
+        public static void Main()
+        {
+            using var mutex = new Mutex(false, ApplicationKey, out bool createdNew);
+
+            if (createdNew)
+            {
+                var application = new App();
+
+                application.InitializeComponent();
+                application.Run();
+            }
+            else
+            {
+                var currentProcess = Process.GetCurrentProcess();
+                var mainProcess = Process.GetProcesses()
+                    .Where(x => x.Id != currentProcess.Id)
+                    .FirstOrDefault(x => x.ProcessName == currentProcess.ProcessName);
+
+                if (mainProcess != null)
+                {
+                    ShowWindow(mainProcess.MainWindowHandle, RestoreWindowCommandCode);
+                    SetForegroundWindow(mainProcess.MainWindowHandle);
+                }
+            }
+        }
+    }
+}