fixed a bug with ActionBar appearance on screen orientation change

This fixes the [issue #174](https://github.com/umano/AndroidSlidingUpPanel/issues/174).

How DemoActivity handles the ActionBar appearance is a bit inconsistent - `getActionBar.hide()` and `setActionBarTranslation(float)`  in no way lead to the same ActionBar state.  Thus, a call to `getActionBar.hide()` should be replaced to the latter.

`!getActionBar().isShowing()` in `onSaveInstanceState(Bundle)` always result to false, thus the ActionBar is considered shown even if a panel is expanded, and is not hidden on orientation change.

I made SlidingUpPanelLayout a class member variable, which allows to check its state in `onSaveInstanceState(Bundle)`.

When restoring the state, if we consider that ActionBar should be hidden, then we call `setActionBarTranslation( - actionBarHeight )`, thus moving away the ActionBar.