DUI: icons for class buttons, method buttons, tooltips.

This PR was made to implement Small icons for class buttons & method buttons; Large icons for tooltips.
# Before
![image](https://cloud.githubusercontent.com/assets/8158404/4057010/ea287b00-2dc2-11e4-899b-03e68c08ae5b.png)

# After
![image](https://cloud.githubusercontent.com/assets/8158404/4057012/eebb7884-2dc2-11e4-9218-5c9633fb817b.png)

Pay attention