Maint: add Container.components setter.

[jonathanrocher]

In Chaco's implementation of the BasePlotContainer, a warning states that getting or setting plot_components is deprecated, and components should be used instead. But enable's Container class doesn't have a setter for the components property.

This PR corrects that.

[codecov-io]

Codecov Report

Merging #387 into master will not change coverage.
The diff coverage is 70.58%.

@@           Coverage Diff           @@
##           master     #387   +/-   ##
=======================================
  Coverage   32.73%   32.73%           
=======================================
  Files         206      206           
  Lines       18297    18297           
  Branches     2470     2470           
=======================================
  Hits         5990     5990           
  Misses      11929    11929           
  Partials      378      378

Impacted Files	Coverage Δ
enable/trait_defs/rgba_color_trait.py	0% <ø> (ø)	⬆️
enable/savage/trait_defs/ui/qt4/svg_editor.py	0% <0%> (ø)	⬆️
kiva/fonttools/font_manager.py	50.59% <92.3%> (ø)	⬆️
enable/toolkit_constants.py	100% <0%> (ø)	⬆️
enable/qt4/constants.py	90.47% <0%> (ø)	⬆️
enable/qt4/scrollbar.py	77.22% <0%> (ø)	⬆️
enable/qt4/image.py	75% <0%> (ø)	⬆️
kiva/qpainter.py	51.07% <0%> (ø)	⬆️
enable/qt4/base_window.py	51.07% <0%> (ø)	⬆️
enable/component_editor.py	79.16% <0%> (ø)	⬆️
... and 10 more

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[jvkersch]

LGTM!

Perhaps a small test to exercise getting and setting components?

[jonathanrocher]

Thanks for approving the change @jvkersch . I added a unit test to exercise the setter. Further comments/reviews welcome.

[jonathanrocher]

This has been sitting approved for a while, so I will merge soon unless there are more comments.