Player auto stop at the end

[bfarago]

Enhancement from earlier backlog:
-File veget lejátszva auidio buffert előbb szüntetjük meg mint ahogy a windows wdm
befejezné a buffer feldolgozást. Meg kell várni mig leállt a hang...

When the player reaches the end of the "program" or file, then player stops playing too early. It should wait for the WDM finish the all buffer in the pool.
Probably fix: two statemachines should have: one for the application, and one for the player task, which administer the WDM in the background. So, two kind of stop is needed: stop immediate (like pause, or stop by user interaction) and auto stop at the end, when player waits til the end. UI keeps playing while last buffer processed, while new buffer shouldn't fill (or fill with silence?).