<ADD: BTTree can be loaded and saved via Serializing system now>
<ADD: basic drawing function of BTTreeViewer in BTTreeEditor>
<ADD: Rectangle in BTTreeViewer can be dragged by mouse now>
<ADD: BTEditorRectangle can be clicked and the corresponding BTNode can be observed in Attribute Panel.>
<ADD: Add scrollbar to BTTreeViewer>
<TODO: Summarize the way to add scrollbar to customized controller>
<ADD: change edge, sequence of node and remove subtree of bttree>
<ADD: you can create new node in bttreeviewer>
<ADD: now you can observe blackboard dynamically in BTTreeEditor now!>
<ADD: BTTreeEditor can observe bttree dynamically now!>
<ADD: create new, open and synchronize all in BTTreeEditor>
<MOD: BTTreeEditor can hide and show now>
<MOD: finish reviewing BTTreeEditor and BTTreeViewer>