FEATURE: Support for App Shortcuts Menu (PR #9749)

This adds a list of shortcuts to a installed Discourse instance.

It can be accessed by right clicks or long press on the app icon.

See https://github.com/MicrosoftEdge/MSEdgeExplainers/blob/master/Shortcuts/explainer.md

List of possible follow ups include:

  • Making it admin customizable
  • Making it user customizable
  • Using SVG icons from the site icon sprite (cc @pmusaraj )
  • Picking an accent color for icons