#28 PlayAll Added to libraries

[Max Metral]

A command has been added to play all the results from
a search, not just what is on screen. It's quite
complicated given the possibility of someone
inadvertently adding 100s of songs which would take
forever to queue... It tries to be nice to the AT, backing
off to 10 seconds between queues after 10 queues, and
also using some fancy signalling to abort "wasted" play
requests when a new play request comes later in the
queue.