renamed test.gst to simpletest.gst

we simply link 'streamtest.gst' or 'simpletest.gst' or whatever to 'test.gst'
initialize live/preview outputs to None
dummy `liveOut` that is uses the 'preview' tag

Closes https://github.com/iem-projects/striem/issues/9

(well, it's rather a hack to circumvent issue #9)
more scalable getWindow() code
remove dummy "live" output from pipeline
remove scaling for output

`xvimagesink` does the scaling on it's own, and so we get the best quality
nicer bettern (moving ball)