Add possibility to browse and open files outside of vaults

## Basic Info

I'm using Android in version: 9.0

I'm running Cryptomator in version: 1.4.2

## Description

The app only allows browsing files and directories located in vaults, but not all my files are stored there, because sometimes I need to share stuff with others. In order to access those files I have to use the cloud provider's website or app. It would be great to be able to access all my files in the cloud from one single app.