Monitor._post_draw: fixed auto-starting animations

    - some backends automatically start the animation on fig.canvas.draw_idle()
NDSDataSource: add parsing of NDSSERVER variable

    - allows auto-check of control room NDS server
NDSIterator: added pad keyword argument
SpectrumMonitor: accept figure kwargs
sync_clock: moved into method

    - sync still doesn't work well with NDS
    - should be ignored by other data sources, probably