Automatic/easier update procedure

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### Feature description

I noticed today how complicated the updates for Nextcloud clients are. For the technically interested (like me), the manual update is relatively simple.

However, if you are a normal user, you don't know such complicated updates from Dropbox or similar. It happens in the background or is just a click (+UAC on Windows).

I think such things of user-friendliness are important if you want to spread OSS and prevent them from simply using Dropbox, etc. again.