feat: Whitelist URL feature.

In the configuration, `max_duration` can be set to prevent
long song(URL item) being downloaded and added to the
playlist.
This whitelist feature provided a way to override this
duration check: songs being whitelisted will be added to
the playlist no matter how long they are.
Three admin commands are introduced:
 - !urlwhitelist (!urlw)
 - !urlunwhitelist, (!urlunw)
 - !urlwhitelistlist, (!urlwls).

 Also, if one song fails due to its length, the bot will
 show the length of this song and the max length limit in
 the reply message.

 Implement #173, #196.

lang/fr_FR.json

@@ -61,13 +61,13 @@
         "shortlist_instruction": "Utilisez <i>!sl {indexes}</i> pour jouer l'élément que vous voulez.",
         "start_updating": "Début de la mise à jour...",
         "stopped": "Musique arrêté.",
-        "too_long": "<b>{song}</b> est trop long, supprimé de la playlist !",
+        "too_long": "<b>{song}</b> est trop long ({duration} > {max_duration}), supprimé de la playlist !",
         "unable_download": "Impossible de télécharger <b>{item}</b>. Retiré de la bibliothèque.",
         "unable_play": "Impossible de jouer <b>{item}</b>. Retiré de la bibliothèque.",
         "unknown_mode": "Mode de lecture \"{mode}\" inconnu. Il devrait s'agir d'un des modes suivants : <i>one-shot</i>, <i>repeat</i>, <i>random</i>.",
         "update_successful": "<h2>botamusique v{version} Installé ! </h2><hr />\n<h3>Changelog</h3> {changelog} <hr /> Visitez <a href=\"https://github.com/azlux/botamusique\">notre repo github</a> pour plus de détails !",
         "url": "URL",
-        "url_ban": "Cette URL est interdite !",
+        "url_ban": "URL {url} est interdite !",
         "url_from_playlist": "URL",
         "url_from_playlist_item": "<a href=\"{url}\"><b>{title}</b></a> <i>depuis la playlist</i> <a href=\"{playlist_url}\">{playlist}</a> <i>ajouté par</i> {user}",
         "url_item": "<a href=\"{url}\"><b>{title}</b></a> <i>ajouté par</i> {user}",