Integrate platform info into launcher

[jdrueckert]

Currently, the launcher has no information about for which platform it was built. Thus, we cannot self-update as we don't know which asset to download. We need a way to integrate the information for which platform we build it into the launcher at build time so that the launcher can access that information on runtime.

Discussion result: the launcher is to detect OS and arch during startup

With this information, the self-updater can download the matching asset.
We do need to make very clear which OS and arch it updates to in the dialog(s) and logs, though.