* all: first support of graphical equalizer in the skins2 interface.

* all: first support of graphical equalizer in the skins2 interface.
  It can be defined in the XML with usual sliders, using the new
  variables equalizer.band(0), ..., equalizer.band(9)
  (0% means -20dB, and 100% means +20 dB).
  More things to come, but it is already working as is.
* all: AsyncQueue::push() now does also a remove() by default, as
  the two methods are always called together