Show/hide ImageView side histogram

[vallsv]

This MR provide an API to show/hide the side histogram of the ImageView.

It is added as a tool in the toolbar, and a new entry in the (image view main window)

Changelog:

• Added an action to show/hide the side histogram of the ImageView
• Few clean up around ImageView module
• Update the imageview example with a --live option
• Added resetzoom to ImageView.setImage

[vallsv]

I have replaced layout.addWidget(self._histoVPlot.getWidgetHandle(), 0, 1) by layout.addWidget(self._histoVPlot, 0, 1).
I think it only makes sens for the main widget.

[t20100]

I have replaced layout.addWidget(self._histoVPlot.getWidgetHandle(), 0, 1) by layout.addWidget(self._histoVPlot, 0, 1).

Sounds good. I think it was there to really make sure there is no additional margins in PlotWidget which would make the histograms not aligned with the image plot, but it should not be needed.

I'd move ShowSideHistogramsAction outside of silx.gui.plot.actions since all actions in silx.gui.plot.actions are compatible with PlotWidget.
I would put it as a private class in ImageView.py as it is only used there, else eventually in a dedicated module in silx.gui.plot.actions.

[vallsv]

This can be reviewed.

I did some cleanup around the ImageView.

The main weird change is the setStartusBar(None) that i have removed. This was creating blinking cause just before it is set to something. So i dont know if it have to be displayed or not.

The other change is the use of setImage(resetzoom), instead of reset, for consistency with the other plot API. I don't like much the resetzoom, but i think it is better to be share the same API. reset is still working.