resource-chooser -- Create a resource chooser to replace file chooser somewhere

[deyan]

Create a resource chooser

• The resource chooser should be a dropdown
• The resource chooser should list all of the resources of a kind (or some kinds)
• The resource kinds should be selectable by developers. Resource chooser should allow different kinds of resources to be listed in the dropdown.
• At the bottom of the list there should be a <Browse...> item preceeded by a separator that should open a file dialog
  • If only one resource kind is chosen, the dialog should be for this resource kind
  • Else the dialog should be for all files.
• Put the resource chooser in
  • Book Properties dialog - to choose background audio
  • Frame/page image background