Add LaunchBox clear logo provider to Extra Metadata Loader

[mjd4219]

Summary

• Adds LaunchBox as an additional clear-logo source for Extra Metadata Loader on the emlCrashFix2025 release branch.
• Uses LaunchBox Metadata.zip to build a local clear-logo cache and downloads images through the LaunchBox image CDN.
• Adds a manual LaunchBox logo download menu item and an opt-in automatic/library-update setting.
• Adds only the new English localization strings in en_US.xaml, per maintainer guidance.

Validation

• Built source/Generic/ExtraMetadataLoader/ExtraMetadataLoader.sln in Release from the emlCrashFix2025 checkout.
• Build completed with 0 errors. The branch still emits the existing Magick.NET x86/MSIL warning.
• Packaged with Playnite Toolbox as ExtraMetadataLoader_705fdbca-e1fc-4004-b839-1d040b8b4429_1_87.pext.
• Manually tested the packaged extension in Playnite; LaunchBox logo download completes and downloads logos successfully.

[mjd4219]

Packaged .pext for easy manual testing is available on my fork release:

https://github.com/mjd4219/PlayniteExtensionsCollection/releases/tag/emlCrashFix2025-launchbox-clear-logo-test-1

Package: ExtraMetadataLoader_705fdbca-e1fc-4004-b839-1d040b8b4429_1_87.pext
SHA256: A83832A32118C232E339C1113B596B526D2B103E031AA65F5E89FBD029BCF44B