Media::Player::Widget displays the current voice / video message
if it is played and the current song otherwise.
It is created when a voice / video message starts and is destroyed
when all the voice / video messages in the playlist are finished.
Currently the build without implicitly included precompiled header
is not supported anyway (because Qt MOC source files do not include
stdafx.h, they include plain headers).
So when we decide to support building without implicitly included
precompiled headers we'll have to fix all the headers anyway.
