iOS Extension Support

### Description
In the iOS 15, support for Safari extensions was added. It would be interesting to have an iOS app/extension to use on iOS Safari.

### Environment (if bug)

* Octotree version: n/a
* Browser & version: Safari
* OS & version: iOS 15
* Screenshot, if any (drag an image here) n/a
* Console error log below this line
n/a
