take list headers into account
allow null item, Useful to show empty section but still show the header
newHeader should be the added one
if the listview has headers make sure the headerPosition is >= 0
Merge branch 'master' of github.com:Akylas/StickyListHeaders into reuse_header

Conflicts:
	library/src/se/emilsjolander/stickylistheaders/StickyListHeadersListView.java