* Add split size GUI widget
* Set split size and save GUI widget state in settings
* Set max split size in GUI to 600 MB
* Move chunk size control in middle column and widget on panel below.
Added warning label and tooltip
* Fix chunk size incorrectly enabled when webtoon active and format change
* add 'on older ereaders'
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Co-authored-by: Alex Xu <alexkurosakimh3@gmail.com>
