Fix bug: new bone models have 'parent' field as 'null'
Fix bug: 'data.parent' may be 'null', so cannot just check whether 'parent' field exists
Change active bone when click time-line, and prevent recursively changing active bone
Support manually add & remove keyframe, if the keyframe removed is displaying, use tween frame render to bone-prop & workspace panel
Delete spare method
Support changing texture, and auto load the image selected by user
Add image resource: texture for demo
Remove spare style
Exchange place of add-keyframe button & remove-keyframe button
Support delete bone, and sync to model and all panels