Allow the user to modify the song queue in the music plugin

[zylozs]

When you ask for the queue, it should be numbered such as:

Queued Songs:
1. music/oceans_of_glory.mp3
2. music/the_stage.mp3
...

You should be able to use a command to add a song at an index such as:

!m next blessed 2 (with overloading)
!m nextat blessed 2 (without overloading)

You should also be able to use a command to remove a song/s at an index/es or by name such as:

!m remove oceans_of_glory (or call it dequeue?)
!m remove 1
!m remove 1,3
!m remove 1-3

If there are multiple instances of the song with the name, tell them to specify an index or to add a condition such as:

!m remove oceans_of_glory 1,3
!m remove oceans_of_glory all