Enhance Windows installer configuration and add license file

- Updated the WiX configuration in build_windows.py to include required properties for the WixUI_InstallDir dialog.
- Changed the UI reference from WixUI_Minimal to WixUI_InstallDir for improved installation experience.
- Added custom branding images for the installer UI using WixVariable for background and banner images.
- Introduced a new license.rtf file containing the MIT License for the WebDrop Bridge project.
- Updated binary resources for background and banner images.

build/WebDropBridge.wxs

@@ -8,15 +8,19 @@
         <Package InstallerVersion="200" Compressed="yes" InstallScope="perMachine" Platform="x64" />
         <Media Id="1" Cabinet="WebDropBridge.cab" EmbedCab="yes" />
         
+        <!-- Required property for WixUI_InstallDir dialog set -->
+        <Property Id="WIXUI_INSTALLDIR" Value="INSTALLFOLDER" />
+        
         <!-- Application Icon -->
         <Icon Id="AppIcon.ico" SourceFile="$(var.ResourcesDir)\icons\app.ico" />
         
-        <!-- Embedded branding images for installer UI -->
-        <Binary Id="BannerBmp" SourceFile="$(var.ResourcesDir)\icons\banner.bmp" />
-        <Binary Id="DialogBmp" SourceFile="$(var.ResourcesDir)\icons\background.bmp" />
+        <!-- Custom branding for InstallDir dialog set -->
+        <WixVariable Id="WixUIDialogBmp" Value="$(var.ResourcesDir)\icons\background.bmp" />
+        <WixVariable Id="WixUIBannerBmp" Value="$(var.ResourcesDir)\icons\banner.bmp" />
+        <WixVariable Id="WixUILicenseRtf" Value="$(var.ResourcesDir)\license.rtf" />
 
         <!-- Installation UI dialogs -->
-        <UIRef Id="WixUI_Minimal" />
+        <UIRef Id="WixUI_InstallDir" />
         <UIRef Id="WixUI_ErrorProgressText" />
 
         <Feature Id="ProductFeature" Title="WebDrop Bridge" Level="1">