Close button in toolbar UI for physically disabled persons (ticket #4328)

Hello,
I've added a close button in toolbar after the "step" button and before the "volume" button. 
I've checked mph working on Windows XP Professional, Windows 7 x64 and Windows 10 Preview x86.
Hope everything is ok.
Ticket:: https://trac.mpc-hc.org/ticket/4328#no4