BUG: Fix Extension Wizard to write icon files correctly on Windows
requested to merge github/fork/msmolens/4027-slicer-extension-wizard-handle-binary-files into master
Created by: msmolens
On Windows, slicerExtensionWizard creates invalid icon files for extensions and modules. This happens because the script treats all template files as text when opening them to replace the template key, including the PNG icon files.
This changes the script to open and write files in binary mode.
Fixes #4027.