Implemented Infinite Canvas

By using the following technique to simulate the infinite canvas with grid line.
![image](https://f.cloud.github.com/assets/5276243/1201426/9cb282ae-2534-11e3-8418-9a28ec22b52c.png)

Changes include:
- New Grid Line Design
- Allow nodes to be outside its container (DragCanvas)
- Updated Canvas Control for current implementation (ZoomBorder)