Made whiteboard shapes and text editable

This branch is based on the 0.81 beta 2 version. Shapes and text on whiteboard can be re-sized, moved, edited and deleted. After selecting a text, holding Ctrl key and click and the text again with change the text to edit mode.

Stroke is zoom-able. When user zoom in, not only shapes look bigger, their strokes are also thicker. If the stroke is small, it's hard to select the shape. Use can zoom it to select it.