Fix Overlay menu size

fix for https://github.com/jsk-ros-pkg/jsk_visualization/issues/190

* change the size of menu according to the change of title
* fix window position if the window is larger than the rviz

![screenshot_from_2014-11-03 13 33 57](https://cloud.githubusercontent.com/assets/40454/4878591/a62516d6-6312-11e4-89d8-90a38c75758f.png)