Comment 12 for bug 367151

This patch is against r2970.
Apart from improving my implementation in WGLWaveformViewer::eventFilter(), changes are as follows

1. Increased zooming
2. Pre-roll doesn't zoom any more
3. Pitch slider doesn't affect zoom
4. new COs for adding '+' and '-' zooming buttons on skin
    - new COs are 'zoom_waveform_in' and 'zoom_waveform_out' for zoom in and zoom out resp.
    - I am also attaching a dummy skin.xml from Deree 1280x800 WXGA which uses these new COs to control zooming from
      Raise/Lower pitch buttons on Channel 1