bar_overflow_distance

Luka, I don't think in the hidden state contentView height should be extended by barOverflowDistance. Ofc it simplifies animation code but it's not what the user usually wants (so far I can't find a scenario for this behaviour to be useful).
Now barOverflowDistance is used only in animating the bar itself but not the contentView. To make animation look properly it's now splitted in 2 parts:
1. contenvViewAnimation + bar animation w/o barOverflowDistance
2. bar animation with barOverflowDistance

So f.e. if bar is hiding first 1st animation is followed by animation 2nd are performed. If bar is showing 2nd animation is followed by the 1st one.

Also this pull request includes some Petr's code that you have discussed in his pull request.
You should always leave an empty newline at the end of files, helps for git.