As a user I should either see whole filter view or see no filter view at all

[Augustyniak]

Similar behavior is implemented in many applications, for example in ICloud Drive.

Acceptance criteria:

1. Aftter user stops scrolling in the directory view and filter view is partially visible we should: 1. Hide filter view if only half of the search bar is visible. "Hiding" should be accomplished simply by changing contentOffset of UICollectionView 2. Show the whole filter view otherwise. This should be also implement by proper adjustment of contentOffset of UICollectionView.