Add Inventories app

[alicerunsonfedora]

This PR makes the following changes:

• Introduces Inventories, an app designed to let developers and players work with an inventory system quickly.
  • Introduces ASInventoryItem class that works with Inventories.
  • Includes the main app as well as an optional HUD that players can use to quickly access items. Depends on developers' preference
• Add insensitive background to ASInterfacePushButton in ScreenKit
• Update documentation to include Inventories docs and fix the System Info icon in Default Apps.

[gitpod-io-legacy-app]

Open in Gitpod - starts a development workspace for this pull request in code review mode and opens it in a browser IDE.

[sr229]

I wouldn't recommend this kind of icons moving forward though. I suggest a custom icon set for this kind of stuff.

[alicerunsonfedora]

Noted, though the icons here do not come bundled with the app. The only one that's bundled is the gift one. This uses the same icon set, Feather Icons. When there isn't an icon from there, Material is used.

Rather, the icons in the screenshot are just placeholders to indicate that you can customize the image preview/icon with the imageName parameter.