Add option to Add subreddit to Home Screen as shortcut

[acolombo11]

As per discussion #982.

Here is a video recording demonstrating how it works: https://github.com/Docile-Alligator/Infinity-For-Reddit/assets/9468299/31bce3ef-21e4-41b3-9ae2-583abd301383

[vishalnandagopal]

Thank you for implementing it!

[acolombo11]

@Docile-Alligator I updated the pull request adding the null check you requested, also check my other comments I left ;)

[Docile-Alligator]

Thank you!