Add 'voteskip' command to vote to skip currently playing song.

[tgoins]

Giving everyone the ability to skip isn't always the best thing. A fair skip mechanism to prevent abuse of the skip command is to only people to vote to skip, then if the vote reaches a certain number, the song will be skipped.

Need to add a threshold to determine either the ratio of people in the voice channel, or a set number of votes required in order for the song to skip.

The votes should be tied to the user, to prevent someone from double-voting. The votes should reset once the song ends or is skipped.