Add single repeat (#359)

* Add single repeat mode

* Toggle between NONE and REPEAT modes when no argument has been given

* Allow single as repeat mode

* Add one to the arguments

* Add backwards comparability for old versions of MusicBot.

* Use JSONObject#getEnum for parsing repeat mode

* Rename repeat modes & fix repeat one not repeating properly

* Add copyright notice & author to RepeatMode

* Fix spacing in SettingsManager

* Rename REPEAT_ONE to One in RepeatMode

* Rename repeat to repeat_mode

* Use variable on track end in AudioHandler & update RepeatMode & its usages

* Use user friendly name in RepeatCmd

* Remove unused constants

* Fix spacing in SettingsManager

* Rename repeat modes to off/all/single respectively

src/main/java/com/jagrosh/jmusicbot/commands/general/SettingsCmd.java

@@ -18,6 +18,7 @@ package com.jagrosh.jmusicbot.commands.general;
 import com.jagrosh.jdautilities.command.Command;
 import com.jagrosh.jdautilities.command.CommandEvent;
 import com.jagrosh.jmusicbot.Bot;
+import com.jagrosh.jmusicbot.settings.RepeatMode;
 import com.jagrosh.jmusicbot.settings.Settings;
 import com.jagrosh.jmusicbot.utils.FormatUtil;
 import net.dv8tion.jda.api.EmbedBuilder;
@@ -59,7 +60,9 @@ public class SettingsCmd extends Command
                         + "\nVoice Channel: " + (vchan == null ? "Any" : "**" + vchan.getName() + "**")
                         + "\nDJ Role: " + (role == null ? "None" : "**" + role.getName() + "**")
                         + "\nCustom Prefix: " + (s.getPrefix() == null ? "None" : "`" + s.getPrefix() + "`")
-                        + "\nRepeat Mode: **" + (s.getRepeatMode() ? "On" : "Off") + "**"
+                        + "\nRepeat Mode: " + (s.getRepeatMode() == RepeatMode.OFF
+                                                ? s.getRepeatMode().getUserFriendlyName()
+                                                : "**"+s.getRepeatMode().getUserFriendlyName()+"**")
                         + "\nDefault Playlist: " + (s.getDefaultPlaylist() == null ? "None" : "**" + s.getDefaultPlaylist() + "**")
                         )
                 .setFooter(event.getJDA().getGuilds().size() + " servers | "