starting with precalculated color tables in spectrograms


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@2103 29e17f8d-cf37-471e-a288-72cc03a76eda
spectrogram example extended


git-svn-id: svn://svn.code.sf.net/p/qwt/code/trunk@2104 29e17f8d-cf37-471e-a288-72cc03a76eda