Allow individual parameters to be changed

[bparks13]

Instead of requiring all parameters to be filled out and then subsequently written to a channel, this update now allows only those parameters that are filled in to be applied to a channel or channels.

For example, instead of having to fill out all timings and amplitudes, if the pulse width is the only parameter that needs to be updated, the pulse width is the only variable that is filled in when Apply is pressed.

Added additional checks if the pulse is biphasic symmetric to ensure consistency.

• Fixes Rhs2116 Stimulus Sequence Dialog - Change individual parameters across all channels #344

[jonnew]

This looks really good. I like the behavior a lot. The only critique I have is that the plot zoom resets when parameters are changed. The reason this is a bit annoying is because for a sequence I'm zoomed in to the portion of the waveform that I want to change. When I go edit e.g. an amplitude parameter and expect to see the at change reflected in the waveform, the view resizes and I have manually zoom in again to see if my change had the indented effect.

If there is a way to save the zoom state and reapply when parameters are changed, I would like that. Otherwise, this looks very good.

[bparks13]

@jonnew I have created a new issue regarding saving the zoom state (#349), feel free to add any more thoughts to the issue. For now, I have set it as the 0.5.0 milestone, but we can push for it to be 0.4.1 if we fully define the problem quickly.

There is a very related issue (#313) that can also be fleshed out at the same time related to resizing dialogs.