Remember subplot adjustements on redraw

[ebranlard]

Reproduce:

• change the left/right/top/bottom margins
• draw another channel
• the margins are not remembered, which is annoying

see also #65

[ebranlard]

Note: the parameters can be obtained as follows:

    params = self.canvas.figure.subplotpars
    paramsD= {}
     for key in ["left", "bottom", "right", "top", "wspace", "hspace"]:
            paramsD[key]=getattr(params, key)
            self.canvas.figure._subplotsPar = paramsD

The are changed dynamically by the SubplotTool of widgets.py.

The subplot tool is launched by NavigationToolBar2.configure_subplots(self, *args) There is a hook, when the subplot window is closed that we can use to setup a trigger, e.g.:

    tool_fig.canvas.mpl_connect("close_event", close_event)

[ebranlard]

Spacings stored in class on draw event, before deleting the figure.