Update app.cpp

Hello,

I look for a way to run a playlist from command line. I did not find how obtain this behavior without changing source code.
 
Also I need possibility to run playlist by url from command line. So I add quick-and-dirty fix for this too. I looked at GetUrlDialog and Downloader but I can't quick figure out how to reuse it correctly.

So I am not pretend that you taking this patch, but I will happy if you add described functionality for next relises.

Sorry for my english.