skal authored Nov 24, 2016 and Jehan committed Nov 26, 2016

webp-save: Add UI elements for 'minimize size' toggle, and a dependent
'max key-frame distance' setting.
* If 'minimize size' is active, max-kf is disabled (which is equivalent to
  setting it to infinity). Key-frame cost file size, that's why.
* If 'minimize size' is disabled, you get to choose how far key-frames
  (=cue points) will be inserted at max.