cubicweb #1112781 box: change to a new useful tooltip convention [deprecated]

In box widget, we display __regid__ as default action tooltip. Maybe, we could create a new tooltip attribute to replace that.

Whatever, we should not confuse users by technical implementation details as __regid__.

Related coded in, action)

Patch ready for inclusion: feature-1112781-new_tooltip_default.diff in juj's branch

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