cubicweb #2067564 Capture errors as locally as possible [open]

When an error occurs while generating the page, the error-template displays the corresponding traceback. But quite often, the error happens while generating a small component (a box, a ctxcomponent, etc.) It would be nice, at least in non-debug mode, to have the traceback displayed in place of the faulty box (or component or ...) and let the other parts of the page be rendered normally. The main idea is to try to display as much as possible of the asked page.

If the print-traceback option is set to no, a special <div> with a report bug button would be inserted.

The difficulty is to define where to add try: ... except: ... statements in the execution flow, we definitely don't want to add it blindly on appobject.render().

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