* #3593: render_frame and render_preview tile `times` into one contact sheet
* contributors: credit andreaaazo by their GitHub profile name
* #3593: contact-sheet cells default to 320 px, sheets stay under 8000 px
With `times`, `max_side` now defaults to 320 per cell instead of 960, so
64 frames of a 16:9 comp make a 2560 x 1440 sheet instead of 7680 x 4320.
`sheet::MAX_SIDE` drops from 8192 to 7680. `labels` that isn't true or
false is a bad-arguments error, and a bridged cell keeps the time asked
for when the app's reply leaves `time` out.