Use LaunchAgent for start at login on macOS 12 & fix image dpi

[gnattu]

Main changes:

• Now it will detect the folder it runs from and will refuse to start when not being put into the Applications folder, as that may lead to various problems
• Bumped the package version to let the macOS system register this specific package to resolve potential conflicts on launch at login, as older versions can still run at arbitrary locations and macOS could start a random one if they have the exact same package version.
• The old mechanism we used for start at login no longer works on macOS 12 and the macOS 12 system API is awful to use. I tried multiple times with the LaunchAtLogin module we are using, and I cannot make it reliably to restart on login in a macOS 12 VM. Instead, I wrapped the LaunchAtLogin model to implement launch at login with custom LaunchAgents. This approach will not be compatible with sandboxing, but the jellyfin server itself is not compatible with sandboxing either, so there is no need to be concerned.
• Provided scaled logo banner for different DPI monitors to fix the awful scaling on low DPI monitors:

Before:

Now:

Fixes #39

Fixes https://forum.jellyfin.org/t-démarrage-de-jellyfin-automatiquement-avec-le-mac