Access all apps from the Nextcloud app

### Is your feature request related to a problem
it is totally frustrating and incomprehensible for users that there is a next according to the app but not all functions can be accessed from this app but only via the browser.

### Describe the solution you'd like
that all apps are accessible via the Nextcloud app. This can be achieved by opening the respective apps via the in app browser. Just as it is handled in the external sites app.

### Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

### Additional context
Add any other context or screenshots about the feature request here.

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