rqt_reconfigure: Removing unnecessary margins which make rqt_reconfigure useless on small screens

This removes all the extra padding from rqt_reconfigure. It makes it usable on small screens.

In the attached image, the current version is above, and the patched version is below. Each window is given the same exact screen space:

![rqt_reconfigure_compact](https://cloud.githubusercontent.com/assets/1253450/2989586/91339f56-dc65-11e3-8c71-312d3a47e776.png)