PreviewBubble implementation

Due to a lot of merge conflicts with master I create a new branch from master and copy the necessary code on top of it.

Implement preview for nodes
-Preview bubble can be in the condensed mode, minimized mode or full mode
-Preview bubble currently show only text preview
-Preview Bubble will update when the value in Node model change
-Preview Bubble can be scroll
-Preview Bubble can be resize

Implement an item at view menu allow switch between 2 stage of preview bubble


![0](https://f.cloud.github.com/assets/5309295/1379873/3bd0e0ee-3afa-11e3-8cc0-da7430380d04.png) ![1](https://f.cloud.github.com/assets/5309295/1379883/607133b8-3afa-11e3-9f7e-d87d76185a03.png) 

![2](https://f.cloud.github.com/assets/5309295/1379875/3bd8c03e-3afa-11e3-9b54-5b9744b2d9c0.png) ![3](https://f.cloud.github.com/assets/5309295/1379876/3bda5200-3afa-11e3-9a2a-4cc3b21e3157.png)