Fixed an error when logging in to Dropbox where the user was logged out again within a short time.
Update of the Dropbox SDK.

- Update to the latest Dropbox SDK
- minor bugs fixed

Updates were made for the libraries used and the UI was adapted for the dark mode. Furthermore, a few minor bugs were fixed.

* Adaptations to iOS 15 and the new iPad mini 6th generation.
* Update of the existing Dropbox SDK to the current version
* Elimination of small bugs that have accumulated over time

In this version a few minor bugs were fixed and internally used frameworks were updated.