Add Apply-Button for the Queue-Manager.

Queue Manager:
-Added Apply button to dialog
-Added an extra SLOT for the Apply button to use
-Refactored the function called when playlist is updated so that adding items uses In list and removing items uses Out list

Playlist:
-Refactored updating Playlist from Queue Manager so Ok and Apply buttons can use same function
-Modified how the In & Out list are generated when queuing selected items
otherwise the Queue Manager receives an incorrect list from the SIGNAL

Patch by Warren Koo Tze Mew.