Set/control number of points in scatter plot by a PV

[prjemian]

• Close Plots: number of points supplied by a PV #608
• Close scatterplot.py needs a unit test suite #842

[codecov-commenter]

Codecov Report

Merging #836 (74cd60d) into master (4f6810f) will decrease coverage by 0.12%.
The diff coverage is 28.57%.

@@            Coverage Diff             @@
##           master     #836      +/-   ##
==========================================
- Coverage   59.94%   59.81%   -0.13%     
==========================================
  Files          95       95              
  Lines       11406    11441      +35     
==========================================
+ Hits         6837     6844       +7     
- Misses       4569     4597      +28     

Impacted Files	Coverage Δ
pydm/widgets/scatterplot_curve_editor.py	36.36% <14.28%> (-4.46%)	⬇️
pydm/widgets/scatterplot.py	29.16% <31.42%> (+0.59%)	⬆️
pydm/widgets/symbol_editor.py	80.51% <0.00%> (-0.37%)	⬇️
pydm/widgets/rules_editor.py	96.08% <0.00%> (-0.31%)	⬇️
pydm/main_window.py	52.20% <0.00%> (-0.28%)	⬇️
pydm/widgets/timeplot.py	70.73% <0.00%> (ø)
pydm/data_plugins/calc_plugin.py	25.54% <0.00%> (+0.13%)	⬆️

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[prjemian]

Noting that no unit tests have been added for this PR. But there is no specific unit test file for scatterplot.py, either.

[jbellister-slac]

Feature looks great! Gave it a spin with some test PVs and it works like I would expect.

[jbellister-slac]

Thank you for the additional tests as well, this looks great to me!

[prjemian]

@jbellister-slac Thanks!