Config overhaul: split tracker mode

[josecelano]

Parent issue: #401
Relates to: #401 (comment)

Tracker privacy (public and private) and torrent restrictions (whitelisted or not) are totally independent options.

Current

pub enum TrackerMode {
    Public,
    Listed,
    Private,
    PrivateListed,
}

[core]
mode = "public"

New Version

[core]
private = true # boolean
listed = true # boolean