Adds live plot context manager and update events

[StephenNneji]

Adds a live plot as a context manager, to use change the controls

controls.procedure = 'simplex';
controls.maxIterations = 100;
controls.updatePlotFreq = 1;

then run like so

with RAT.plotting.LivePlot(block=True):
    problem, results = RAT.run(problem, controls)

or

with RAT.plotting.LivePlot(block=True) as figure:
    problem, results = RAT.run(problem, controls)

[DrPaulSharp]

I can confirm that the plots behave as expected and discussed both when importing and running the examples as a script. I have tested this using both pycharm and the windows x64 command prompt.

Alongside the comments could you please review the test coverage for "plotting.py", in particular could you please write a test for "plot_ref_sld".

[DrPaulSharp]

Whilst we're here . . .
Could we review the axis labels - I used:

ref_plot.set_xlabel("q_{z} (\u00c5^{-1})")
ref_plot.set_ylabel("R(q_{z})") - we could also go for "Reflectivity"
sld_plot.set_xlabel("z (\u00c5)")
sld_plot.set_ylabel("SLD (\u00c5^{-2})")

for my poster. I think they'd be better than what we have. Similarly, for the legend labels, surely it'd be better to use the name of each contrast, rather than "ref 1, ref 2" etc - we could pass them in through the PlotEventData

[StephenNneji]

Is this the intended outcome of the labels or am I missing something? Also are we sure the units will always be Angstrom?

[DrPaulSharp]

Ahh, so close. The ^ and _ are meant to be superscripts and subscripts. good point about units we should check with @arwelHughes, but I'm not aware of how one would change the units in the code.

[StephenNneji]

Also updating the labels via PlotEventData will require me diving into the RAT, C++ to add more stuff so I will do that in another PR but I will update the labels and add a unit test for plot_ref_sld

[StephenNneji]

Ahh, so close. The ^ and _ are meant to be superscripts and subscripts.

This works
ref_plot.set_xlabel("$q_{z} (\u00c5^{-1})$")
ref_plot.set_ylabel("$Ref (q_{z})$")
sld_plot.set_xlabel("$Z (\u00c5)$")
sld_plot.set_ylabel("$SLD (\u00c5^{-2})$")

[StephenNneji]

Is it correct that the unit for Ref is q_z? will that not just be the unit of q_z?

[DrPaulSharp]

Ahh, no I had it that the reflectivity is a function of qz, but obviously it's a bit confusing like this. Maybe best to leave that off then.

[DrPaulSharp]

The strongly recommended way to request fixtures is to include the them in the function arguments. This method of requesting fixtures is for when the choice of fixture depends on other parameters. I've seen that line 554 of "test_run.py" has a line like this as well (no idea who wrote it . . .) - could you please also change that to include the fixture in the function argument.