Add Onion Theme Downloader app

[SebastianMaung]

This app was developed for new users to easily and quickly download themes onto the MMP without having to eject the micro sd card when they wanted to try on something new. I used advance menu and a lot of the code from logotweak for browsing themes. The themes are pulled directly from the theme repo by extracting urls from the readme, and can update without too much of a hassle within 5 minutes. (Instead of being added directly to the package manager it can be added to the community apps instead, this is the original repository)

[Aemiii91]

We should keep this as a community app. Go ahead and add an entry to the wiki 👌