Add callback for setting checkbox state (#908)
Add callback for setting checkbox state (#908)

* Demo of hack for checkbox state

* Fix jsdoc

* Move getCheckboxState into flyout

* Remove other reference to default checkbox state

* Add public to getCheckedState

LLK/scratch-blocks,sclements/scratch-blocks,griffpatch/scratch-blocks,LLK/scratch-blocks,LLK/scratch-blocks,sclements/scratch-blocks,griffpatch/scratch-blocks,sclements/scratch-blocks,gengshenghong/scratch-blocks,sclements/scratch-blocks,griffpatch/scratch-blocks,gengshenghong/scratch-blocks,LLK/scratch-blocks,gengshenghong/scratch-blocks,gengshenghong/scratch-blocks,sclements/scratch-blocks,gengshenghong/scratch-blocks,griffpatch/scratch-blocks,LLK/scratch-blocks,griffpatch/scratch-blocks