Add zen_sort_array() and optimize debug-log widget

Add zen_sort_array() multisort function and apply to debug-log-list widget
- removed duplicate building of logfile array to save memory (used in two places: widget and init-system)
- apply maximum limit to list in widget
- add summary line to log widget

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As per our audio chat, we should consider an early return here
(and make a note to do similar in other places where we do this sort of folder enumeration for other purposes)