PyQwtBiPlot, my (first) PyTauiwi widget

It works!! Finally I improve enough my Python to modify the Fulvio's PyQwtPlot to draw to Tango spectrums attributes in the same plot.

As I wrote before, I need to plot at least to signals to be measured by the timing application. If you need to measure a signal propagation delay, or the jitter, you need to see both at the same time and scale to realize who late the electronics respond to an order.

Thinking in the future, this biplot is prepared to be improved as a multiplot. That is, it has a list of two curves and this value will be easily increased. The old 'FullAttributeName' that now is the spectrum attribute that it is wanted to show will be converted to a list of spectrum attibutes.