Change Dropbox permissions to allow only Cryptomator files

### Basic Info

- I'm running Cryptomator on: Nexus 6P - 7.1.1 Developer Preview 1
- I'm using Cryptomator in veversion 0.2.0

### Description

Instead of requesting full access to the Dropbox account, specify more the permission for only allowing access to the files and folders created by Cryptomator.

> When linking an app to your Dropbox, it will request a specific level of access:
> - Access to its own data. This data doesn't appear in a folder in Dropbox, but it's part of your storage quota.
> - Access to its own folder in your Dropbox. The app will be able to access everything within its folder and know the path to that folder, but won't be able to access any other files or folders in your Dropbox.

(Source: [Dropbox Q&A "What information can a third-party app access when I link it to my account?"](https://www.dropbox.com/help/6231))