[Cinnamon Settings] Changed Hot Corners and Workspaces icons

New Hot Corners icon: 
![overview](https://f.cloud.github.com/assets/1816681/2239614/f240b9ae-9c42-11e3-845f-e481faf24d1f.png)

Renewed Workspaces icon: 
![workspaces](https://f.cloud.github.com/assets/1816681/2239615/02d020ac-9c43-11e3-9671-a9437ba2aeb8.png)