[FIXED JENKINS-20235 JENKINS-20006] Configurable default view

This is PR #4 again without the extra commit, and without the `ModelObjectWithChildren` (will be a separate PR).

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* Make the default view configurable (JENKINS-20235)
* Make the default default view an AllView (JENKINS-20006 -- it looks a bit weird, but that's because AllView looks weird in general)

Untested with real old 1.x data, but at least the test passes.

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I did not implement the ListView-to-AllView conversion, as that can be added at any later time.