setSelection not respect StickyHeader

Hey Emil,

i had some problems with setSelection().

## Expected behaviour
`setSelection(position)` should jump to the listitem. With the listitem below the sticky header.
 
## Actual behaviour 
`setSeletion(position)` to an listitem with a sticky header, the list item is covered by the sticky header

## Problem
`setSeletion(position)` doesn't respect the height of hte sticky header if ther is one at the selected position.

## Solution
1. test if there is an sticky listitem at the position
2. add header height to y-offset