Fix for queue ordering issue in the playlist view when using c-d to dequeue a track (issue #4015)

Fix for the queue order problem referred in issue #4015.
When dequeuing a track the executing function wouldn't update the remaining tracks in queue. Now it updates the queuing position of the remaining tracks instantly.
To do that I created a signal that allows to announce the change in the queue (QueueChange).

In the playlist view created a slot that updates the whole view (as qt optimizes it) as discussed in [1], which may be used by other procedures or events if necessary.

That's it. Waiting for feedback.
Thanks!

[1] - [Forum link](https://groups.google.com/forum/?hl=en#!topic/clementine-player/XMLstJKP0rk)
The intention was to abstract of whatever refreshes the view. I thought it might come a time where some changes to this would be necessary, and all related to refreshing would be abstracted in this function, like some temp data structure that is later added that needs to be reset at this time, you just have to update the function and all about "refreshing the view" will be encapsulated. Just my idea.