Fix file selection when filename already exists in local store

This fixes an issue for our use case where if you're selecting a file that needs to be copied to the local store, and that filename already exists, it won't be copied over.

Fix navigation issue when closing dialog

This fixes the issue where the user was navigated to the home screen as opposed to where they were attaching from after cancelling the file selection.

Add support for iOS

This release adds support for choosing files on iOS.