Move status bar creation to mainwin.ui

Among other things,
* fix turtle icons size (20x14 -> 16x16)
* use QIcon states instead of changing the turtle icon ourselves each
  time (unchecked - off, checked - on)
* make speed limit action in tray menu checkable
* simplify status bar buttons drawing and use QToolButton instead of
  QPushButton


git-svn-id: file:///data/workdir/Transmission-svn/trunk@14389 1bcf1a7e-6170-4b50-b784-84ec52b2dec6