Added support for custom slidable view height

At the moment `SlidingUpPanelLaout` doesn't work well if slidable view height isn't set to `match_parent`. For example, setting height to `300dip` in the demo app produces the following result (image on the left - panel is closed, image on the right - panel is opened). 
![before](https://f.cloud.github.com/assets/750374/1607048/c1678868-546b-11e3-83a9-76ee6308e81b.png)
View height is good, but panel position is wrong. I have fixed the issue and it works as expected now.
![after](https://f.cloud.github.com/assets/750374/1607053/54d69ecc-546c-11e3-9541-b500253e2af1.png)