cancel is misleading in widgets

[Denis-de-Bernardy]

this is a rather serious UI issue imho.

Under Design / Widgets, when one clicks 'edit' for a widget, the label says 'cancel'. But upon clicking 'cancel', it is not cancelled, but rather, 'closed'.

the simplest option would arguably be to switch the label to 'close', rather than to make it actually cancel. if we go this path, though, there may be a case against removing the "change" button.

speaking of the latter, the "change" button is misleading as well: if one doesn't actually save changes, the changes are, in fact, lost.

[ryan]

see #5886