Implement an update check

[rladstaetter]

Is your feature request related to a problem? Please describe.
As a distributor of LogoRRR i want to make sure that users are informed if there is a new version for LogoRRR available. For Mac this is already solved via the app store mechanism, maybe #29 solves this for windows. Linux users will then be the only platform where this feature will be activated.

On startup, LogoRRR will open a http connection to https://www.logorrr.app and check if there is a new version available. The API returns the version information, for example 24.1.0. (This number is changed when a new version is being released.)

If the provided version doesn't match the version of the app itself, a window will be shown (along with an option to "not show again") such that a new version is available for download, with a suitable url to download the application.

Downloading should take place via an web browser since users will be accustomed to that.