Added favicon to user_docs (#18060)
Fixes #17971
Summary of the issue:
When loading NVDA HTML documentation in the browser, there's no page icon (favicon.ico).
Description of user facing changes:
The NVDA logo is visible when opening any .html file in the user_docs
Description of development approach:
I added a simple rel="shortcut icon" similar to nvaccess' website using the NVDA logo
which I found here.
I also changed the logic in sconstruct.py to make sure that the favicon is pulled locally in every subfolder and cleaned when running scons -c
