Another update for the UI

Here is another update !
+ Fixed filter frame's hidden state that was not restored when restoring the instance state
+ Moved the filters 'hide system app' and 'filter by permission' from the settings to the filter frame
+ Bigger expand icon for filter section (asked on XDA)
+ Fixed alignment of the items in the filter section
+ Improved the design of the filter frame (asked on XDA) : the corners are less round, the background is now a gradient

![filters2](https://f.cloud.github.com/assets/3890441/983164/a66785a4-0844-11e3-9bda-d4c6b297aac0.jpg)