Implement watchfaces-preview image system

[eLtMosen]

In same fashion as done for the WallpaperPage https://github.com/AsteroidOS/asteroid-settings/pull/39 Implement display of preview images instead of rendering a live view per watchfaces. Impact on page load and scroll behaviour is even bigger then for the WallpaperPage. Video attached.

• Add preview of the user selected wallpaper as additional selection indicator and aid to estimate watchface/wallpaper combination at a glance
• Fade in/out wallpaper behind the selected watchface in 200ms
• Make Checkmark icon more legible by adding a drop shadow
• Align Checkmark in center of page to avoid clipping
• Show preview images from asteroid-launcher/watchfaces-preview/ instead of slowly rendering live views. https://github.com/AsteroidOS/unofficial-watchfaces/pull/59
• Mask the watchface and wallpaper to either round screen or square screen with rounded edges
• In case of non existent preview image(s), show the live view as fallback.

vanilla page load & scrolling

https://user-images.githubusercontent.com/15074193/149632599-bddcc1de-5802-4fed-a9e9-e347857492bd.mp4

Pageload and selection after PR

https://user-images.githubusercontent.com/15074193/149632627-8b64a43e-b32e-49c9-b1fc-a4b0a689410a.mp4

Masking on square screens

Pre rendered PNG vs Qml rendered live view