add sub-commands to -clear

[michael-je]

Add some sub-commands to the -clear command:

• -clear n to remove the n-th song in the queue.
• Change the command for the current functionality of -clear (which clears the entire queue) to -clear all.
• Add in further sub-commands like -clear first and -clear last, for example.

[morgaesis]

I'd suggest -remove N to remove the Nth song. I feel that using -clear here fit worse. I'd like to reserve -clear to bulk-remove either until, from or entire queue