Show a more accurate/granular view of filesystem permissions

[danirabbit]

Problem

Currently we show a view of filesystem permissions that is kind of inaccurate. We only show if an app has requested permission for the entire filesystem or the entire home directory. We don't show however if an app has requested permission for a specific directory like Downloads

Proposal

Filesystem permissions should probably be its own separate section and have some more granular representation of which directories are included. It should be easy to see/toggle which XDG dirs are allowed.

Perhaps there should be some kind of cascading set of revealers or maybe radios or a dropdown or something that's like:

• ( ) Everything
  A reasonable description of what exactly the whole filesystem including OS means and why an app would need that
• ( ) System Folders
  Nearly all folders, not including the operating system or system internals. This includes all users' Home folders
• ( ) Home Folder
  Your entire Home folder, including any hidden folders
• (x) Specific Folders

and then if "specific folders" is checked you get a flowbox of cute folder icons with checkboxes or something

Prior Art

Flatseal shows kind of a separate section and breakdown of locations but its pretty technical and not super easy to toggle XDG dirs:

[hanaral]

@danrabbit I've added a possible change relevant to this issue in #148, which is to section off storage and folder access to another box beside the device-related permissions so that they can be more clearly defined. Possibly(?) they could have specific locations be added and removed in the same way Privacy & Security → History does via inline buttons at the bottom.