feat(update): client-side rate-limit

Describe the feature you want

The app should only check for updates once every x amount of time, for efficiency and privacy reasons (also to avoid server-side rate-limits).

As of now, UAD-NG checks for list+app updates on every startup, and it also checks for app updates whenever the user opens the About view.

IMO, we should set these limits:

• app: check once every 3 weeks
• lists: check once per week

The user should always be allowed to bypass the rate-limit. For lists, they can simply delete the cached version. For the app, I guess clicking the update-button?

Acknowledgements

• This issue is not a duplicate of an existing feature request.
• I have chosen an appropriate title.
• All requested information has been provided properly.