Rhs2116 - save zoom state when writing new stimuli parameters

[bparks13]

First described in #348, the stimulus sequence dialog should save the current zoom state when adding new stimulus parameters so that the user does not need to zoom in on the same spot again to see if the change had the desired effect.

Care will need to be taken that the current zoom state is still within view after replotting; it is possible that the change could have a drastic effect on the total length of stimulus waveform (say by drastically decreasing the inter-stimulus interval), leaving the current view outside of the plotted waveforms.

• In this case, should the zoom state reset to the fully zoomed out default state?