[IMP] project: add button to hide closed sub-tasks

[bastvdn]

project.task form view > sub-tasks notebook > add a 'hide closed tasks' button (in the same style as 'add a line')

Small remark for the JS tests => The behavior of this widget is related to the currentStorage (simply remembers the previous configuration) i do not reset them in the tests so if you run the same Qunit test again in your browser, it'll fails. It seems to work on the runbot but it will be better with localStorage reset before the test. I tried those with a few ways but couldn't succeed to reset the localStorage consistently.

Task-3703563

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[robodoo]

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[robodoo]

@MissingNoShiny draft PRs can not be approved.

[MissingNoShiny]

robodoo r+