Use nested permissions for clarity

For additional ease of setup, it could be useful to redesign the permissions tab to have nested and dependent permissions. For example, "Embed links" and "Attach Files" could be listed as nested permissions under "Send messages". Turning off the master permission would then also turn off all of its nested permissions. However, it would also be possible to turn off individual nested permissions instead.

I think this would help clarify to server admins, for example, that it's pointless to try to grant permission for a role to Embed links, when they are not allowed to Send messages.