Merging qtgui branch-r9068:9837: this ads a qtgui_sink_c and qtgui_sink_f that displays the time, PSD, and spectrogram plots of a signal put into it. It requires qt4, qwt, and qwtplot3d and has not been tested on OSX.

git-svn-id: http://gnuradio.org/svn/gnuradio/trunk@9853 221aa14e-8319-0410-a670-987f0aec2ac5