feat: three playback mode "one-shot", "loop", "random"

fix: bugs when you are on the last item and you want
remove it.

Some tips for testing:
Observe the behavior when you are playing the last
item and you remove the last item, for all three modes.

configuration.default.ini

@@ -38,6 +38,7 @@ admin = User1;User2;
 music_folder = music_folder/
 # Folder that stores the downloaded music.
 tmp_folder = /tmp/
+database_path = database.db
 pip3_path = venv/bin/pip
 auto_check_update = True
 logfile =
@@ -131,6 +132,7 @@ joinme = joinme
 queue = queue
 repeat = repeat
 random = random
+mode = mode
 update = update
 list_file = listfile
 
@@ -183,6 +185,8 @@ database_dropped = Database dropped. All records have gone.
 new_version_found = <h3>Update Available!</h3> New version of botamusique is available, send <i>!update</i> to update!
 start_updating = Start updating...
 file_missed = Music file '{file}' missed! This item has been removed from the playlist.
+unknown_mode = Unknown playback mode '{mode}'. It should be one of <i>one-shot</i>, <i>loop</i>, <i>random</i>.
+current_mode = Current playback mode is <i>{mode}</i>.
 
 help = <h3>Commands</h3>
        <b>Control</b>
@@ -192,6 +196,8 @@ help = <h3>Commands</h3>
        <li> <b>!<u>st</u>op </b> - stop playing </li>
        <li> <b>!<u>sk</u>ip </b> - jump to the next song </li>
        <li> <b>!<u>v</u>olume </b> {volume} - get or change the volume (from 0 to 100) </li>
+       <li> <b>!<u>m</u>ode </b> [{mode}] - get or set the playback mode, {mode} should be one of <i>one-shot</i> (play the playlist
+       once), <i>loop</i> (looping through the playlist), <i>random</i> (randomize the playlist)</li>
        <li> <b>!duck </b> on/off - enable or disable ducking function </li>
        <li> <b>!duckv </b> - set the volume of the bot when ducking is activated </li>
        <li> <b>!<u>duckt</u>hres </b> - set the threshold of volume to activate ducking (3000 by default) </li>