PR: Set parent for Variable Explorer editors so Spyder closes properly

[CAM-Gerlach]

Fix #5696 .

Currently, any window launched from the Variable Explorer (Dataframe Editor, Collections Editor, etc) will cause Spyder to stay open even if the main window is closed, leading to extra resources and cluter, user confusion and general sub-optimal Ux. Therefore, this PR sets that properly to fix it, and additionally adds a specific test for this as well as improves the existing ones to make them less brittle (as this change broke one of them, my own). Also, updated file/section headers to the consistent standard and did a few bits of minor cleanup around lines that were changed.

[ccordoba12]

@CAM-Gerlach, now this one needs a rebase :-)

[CAM-Gerlach]

@ccordoba12 Done. FYI, test_elapsed_time failed several times on the Python 3.6 builds of both AppVeyor and Travis; the AppVeyor build eventually passed while the Travis one failed all three times and I had to restart it, whence it eventually succeeded. Should I submit a PR to play with the timeouts, etc or if necessary just skip it on Py3.6, or do you have a better fix in mind?

[ccordoba12]

I think increasing the timeouts should be enough. Thanks!

[CAM-Gerlach]

I think increasing the timeouts should be enough. Thanks!

@ccordoba12 Done, as a separate PR of course ( #6714 ). Did so on the two tests that were causing issues, along with related tweaks to a few other tests known to be flaky on Linux locally per you and jitseniesen .

Is there anything you need me to change/do on this one, or is it ready to merge? It should have been ready to go aside from the rebase as far as I'm aware.

[ccordoba12]

Thanks @CAM-Gerlach!